Cable Heating - Debate
Contents:
- [F] How effective is substrate heating?
by bhaskar-at-brtph181.bnr.ca (Shaji Bhaskar) (Mon, 31 Jan 1994)
- [F] How effective is substrate heating?
by (e-mail) (Erik D. Olson) (Mon, 31 Jan 1994/1996)
- [F] How effective is substrate heating?
by bhaskar-at-brtph181.bnr.ca (Shaji Bhaskar) (Tue, 1 Feb 1994)
- [F] How effective is substrate heating?
by maa-at-sisd.kodak.com (Mark Armstrong soft) (Tue, 1 Feb 1994)
- [F] How effective is substrate heating?
by dresler-at-cabell.vcu.edu (Dan Resler) (Thu, 3 Feb 1994)
- [F] How effective is substrate heating?
by bhaskar-at-brtph181.bnr.ca (Shaji Bhaskar) (Fri, 4 Feb 1994)
- [F] How effective is substrate heating? {LONG}
by pulliam-at-NREL.ColoState.EDU (Bill Pulliam) ()
- Re: [F] How effective is substrate heating? {LONG}
by uweb-at-hpbidrd1.bbn.hp.com (Uwe Behle) (Wed, 2 Feb 1994)
- Re: [F] How effective is substrate heating? {LONG}
by pulliam-at-NREL.ColoState.EDU (Bill Pulliam) (2 Feb 94)
- Re: [F] How effective is substrate heating? {LONG}
by uweb-at-hpbidrd1.bbn.hp.com (Uwe Behle) (Wed, 2 Feb 1994)
- [F] How effective is substrate heating? {LONG}
by pulliam-at-NREL.ColoState.EDU (Bill Pulliam) (31 Jan 94)
- [F] Heating coil discussion
by booth-at-lvld.hp.com (George Booth) (12 Dec 1994)
- Aerobic high flow substrates
by "Thomas Barr" <tcbiii/earthlink.net> (Wed, 15 Mar 2000)
- substrate circulation rates
by "Roger S. Miller" <rgrmill/rt66.com> (Fri, 7 Jul 2000)
- Cable flow rates
by "Roger S. Miller" <rgrmill/rt66.com> (Wed, 03 Jan 2001)
by bhaskar-at-brtph181.bnr.ca (Shaji Bhaskar)
Date: Mon, 31 Jan 1994
From recent postings on *.aquaria, I get the impression that a lot of
people have bought into substrate heaters. I've been trying to take
stock of the situation, and I have a few problems with the concept.
1. The Dupla guys claim that water seeps up slowly through the
substrate, bringing with it nutrients that the plants need. This is
what they try to simulate with heating cables. I would think that in
most rivers (and, in any body of water that is above the water table)
water flow would be INTO the substrate, not out of it. This water
would be, I suspect, practically devoid of nutrients.
2. Even in stable bodies of water that are level with the water table,
I would think there is very little inflow of water through the
substrate. Why would water flow up throughthe substrate? The only
reason I can think of is evaporation from the lake surface. How does
the rate of evaporation compare with the flow rates obtained with
substrate heaters? Is more better? If so, how much more? Does Dupla
have any valid experimental data to back up their claim?
3. If you use substrate heaters, the gravel is warmer than the water
above it. This is something that does not occur too often in nature.
Is this good or bad? In nature, I would expect decreasing temperature
with depth, and this is not what the heating cables provide.
4. What evidence do we have on the net that substrate heaters actually
work as claimed? George Booth is impressed by them, but he agrees
that he has no hard evidence to support his subjective evaluation. I
seem to remember at least one significant difference between his
Optimum Aquarium setup and his other tanks in addition to substrate
heaters - the lighting. Jeff Frank (I could be wrong about the first
name) had posted some articles a long time ago advocating substrate
heaters. I don't know of any other strong advocates of substrate
heaters on the net.
All things considered, I think the case for substrate heaters is
inconclusive. Comments?
Shaji.
--
----------------------------------------------------------------------------
Shaji Bhaskar bhaskar-at-bnr.ca
BNR, Research Triangle Park, NC 27709, USA (919) 991 7125
by (e-mail) (Erik D. Olson)
Date: Mon, 31 Jan 1994/1996
In article <1994Jan31.171620.9822-at-bmers95.bnr.ca> bhaskar-at-brtph181.bnr.ca (Shaji Bhaskar) writes:
>From recent postings on *.aquaria, I get the impression that a lot of
>people have bought into substrate heaters. I've been trying to take
>stock of the situation, and I have a few problems with the concept.
I "bought in" because it was inexpensive for me, and I like playing with
aquarium hardware.
["Scientific nature is not like substrate heating conditions" insights
deleted... I'm not doing this scientifically, so I can't comment here.]
>3. If you use substrate heaters, the gravel is warmer than the water
>above it. This is something that does not occur too often in nature.
>Is this good or bad? In nature, I would expect decreasing temperature
>with depth, and this is not what the heating cables provide.
Maybe it's not as drastic as seen in most aquaria, where the gravel is a LOT
colder than the water, being exposed directly to the underside of the tank
and the colder surrounding room. I think there's definite evidence of some
plants wanting warm feet (like Barclaya). I remember one post by George
Booth suggesting Crypts may not like the hot feet; however, the Crypts in my
coil-heated tank are flourishing better than in any of my previous ones (
this may also be due to the pseudo-laterite substrate, but I'll have no way
of knowing this).
>4. What evidence do we have on the net that substrate heaters actually
>work as claimed? George Booth is impressed by them, but he agrees
>that he has no hard evidence to support his subjective evaluation. I
>seem to remember at least one significant difference between his
>Optimum Aquarium setup and his other tanks in addition to substrate
>heaters - the lighting. Jeff Frank (I could be wrong about the first
>name) had posted some articles a long time ago advocating substrate
>heaters. I don't know of any other strong advocates of substrate
>heaters on the net.
Count me in as a "cautious but enthusiastic" supporter for now. I won't
know for sure until the tank's been up a year, but the gravel seems very
clean thus far, and the plants are all doing very well.
I think Uwe Behle is a big cable guy, and Dan Resler is probably in about
the same position as myself right now.
- Erik
---
Erik D. Olson (e-mail)
UW Cosmic Ray Laboratory (e-mail)
Seattle, Washington
by bhaskar-at-brtph181.bnr.ca (Shaji Bhaskar)
Date: Tue, 1 Feb 1994
In article <erik.358.2D4D7C76-at-marge.phys.washington.edu> (e-mail) (Erik D. Olson) writes:
>In article <1994Jan31.171620.9822-at-bmers95.bnr.ca> bhaskar-at-brtph181.bnr.ca (Shaji Bhaskar) writes:
>>3. If you use substrate heaters, the gravel is warmer than the water
>>above it. This is something that does not occur too often in nature.
>
>Maybe it's not as drastic as seen in most aquaria, where the gravel is a LOT
>colder than the water, being exposed directly to the underside of the tank
>and the colder surrounding room.
I appreciate the "most" in your sentence above, but "cold feet" can be
helped quite a bit simply by improving water circulation. In my 65F
room, the gravel is at 78F when the water is at 80F. How does your
substrate temperature compare with the temperature of the water?
Shaji
--
----------------------------------------------------------------------------
Shaji Bhaskar bhaskar-at-bnr.ca
BNR, Research Triangle Park, NC 27709, USA (919) 991 7125
by maa-at-sisd.kodak.com (Mark Armstrong soft)
Date: Tue, 1 Feb 1994
In article <1994Jan31.171620.9822-at-bmers95.bnr.ca> bhaskar-at-brtph181.bnr.ca (Shaji Bhaskar) writes:
>From recent postings on *.aquaria, I get the impression that a lot of
>people have bought into substrate heaters. I've been trying to take
>stock of the situation, and I have a few problems with the concept.
>
>1. The Dupla guys claim that water seeps up slowly through the
>substrate, bringing with it nutrients that the plants need. This is
>what they try to simulate with heating cables. I would think that in
>most rivers (and, in any body of water that is above the water table)
>water flow would be INTO the substrate, not out of it. This water
>would be, I suspect, practically devoid of nutrients.
>
>2. Even in stable bodies of water that are level with the water table,
>I would think there is very little inflow of water through the
>substrate. Why would water flow up throughthe substrate? The only
>reason I can think of is evaporation from the lake surface.
>If so, how much more? Does Dupla
>have any valid experimental data to back up their claim?
I not sure if your have readed "Optimum Aquarium". What they found was
many of the stream contained mineral springs which flowed into the
streams. These springs contained many of the nutrients required by
the plants. The springs also flow thru the laterite which supplies
some of the nutrients.
For the "water flow would be INTO the substrate" comment, many of
the Finger Lakes in NY are "aging" very quickly (lakes do have a life spanned,
an aged lake will become overgrown with algae and weeds). What they discovered
is that septic tank systems would flow into the ground water which feed the
lakes. This water was high in nutrients which feed the algae.
This is not prove that all lakes work in this manner, any river or lake
is depended on the local environment. In NY during the spring time, our water
table is about a foot below the surface. The water table in a arid climate
sould be a "little" deeper. The statement "water flow would
be INTO the substrate" needs to be researched for a specific environment.
The "Optimum Aquarium" folks discovered that the water flow is from
the substrate via the mineral springs for the tropical stream they researched.
>
>3. If you use substrate heaters, the gravel is warmer than the water
>above it. This is something that does not occur too often in nature.
>Is this good or bad? In nature, I would expect decreasing temperature
>with depth, and this is not what the heating cables provide.
Once again, have you research this statement? In NY, the frost line
is a couple of feet. If you dig down 3 or 4 feet, the ground tempature
will rise above freezing. The ground temperature will rise as you
go down. If this is false and the temperature decreased, all the ground
water would freeze and there would be no volcano's.
>
>4. What evidence do we have on the net that substrate heaters actually
>work as claimed? George Booth is impressed by them, but he agrees
>that he has no hard evidence to support his subjective evaluation. I
>seem to remember at least one significant difference between his
>Optimum Aquarium setup and his other tanks in addition to substrate
>heaters - the lighting.
The Optimum Aquarium do not give you their research data but the book
is based on there finding. If you read Mr. Booth's articles, they
state that system without substrate heaters suffered over a period
of time. His undergravel filter tank would require a cleaning, his
tank with substrate heaters did not require this cleaning. The Optimum
Aquarium folks also discussed this, their first tank thrived for many
years (it is a large tank, I think aroung 2500 gallons). After a period
of time the tank suffered. My impression was the lack of substrate heater
but I am not sure if the book specific states this was the problem.
My impression with substrate heating is that keeps the substrate healthy.
It produces the "slow" water flow thru the substrate which releases some
nutrients to the plants (laterite) and prevent nasty bacterial from
grow. So I think if you set up a system without substrate heating the
short term results will be the same but will have different long
term results.
>
>All things considered, I think the case for substrate heaters is
>inconclusive. Comments?
>
All things considered, your should at least find some studies to
disprove "case for substrate heaters is inconclusive". Most of the
statement you make are false or inconclusive.
______________________________________________________________
Mark Armstrong
maa-at-raster.Kodak.COM
______________________________________________________________
by dresler-at-cabell.vcu.edu (Dan Resler)
Date: Thu, 3 Feb 1994
bhaskar-at-brtph181.bnr.ca (Shaji Bhaskar) writes:
>In article <erik.358.2D4D7C76-at-marge.phys.washington.edu> (e-mail) (Erik D. Olson) writes:
>>In article <1994Jan31.171620.9822-at-bmers95.bnr.ca> bhaskar-at-brtph181.bnr.ca (Shaji Bhaskar) writes:
>>>3. If you use substrate heaters, the gravel is warmer than the water
>>>above it. This is something that does not occur too often in nature.
>>
>>Maybe it's not as drastic as seen in most aquaria, where the gravel is a LOT
>>colder than the water, being exposed directly to the underside of the tank
>>and the colder surrounding room.
>I appreciate the "most" in your sentence above, but "cold feet" can be
>helped quite a bit simply by improving water circulation. In my 65F
>room, the gravel is at 78F when the water is at 80F. How does your
>substrate temperature compare with the temperature of the water?
I have ~90 watt heating cables covering the entire tank bottom (90gal)
spaced 6cm apart. The cables are on 75% of the time. The temp at the
*surface* of my substrate is the same as the water temperature.
dan
--
Dan Resler
Dept. of Mathematical Sciences email: dresler-at-cabell.vcu.edu
Virginia Commonwealth University
Richmond, Virginia, USA 23284-2014
by bhaskar-at-brtph181.bnr.ca (Shaji Bhaskar)
Date: Fri, 4 Feb 1994
In article <CKJuEr.Fnu-at-raster.Kodak.COM> maa-at-sisd.kodak.com (Mark Armstrong soft) writes:
>In article <1994Jan31.171620.9822-at-bmers95.bnr.ca> bhaskar-at-brtph181.bnr.ca (Shaji Bhaskar) writes:
>>All things considered, I think the case for substrate heaters is
>>inconclusive. Comments?
>>
>All things considered, your should at least find some studies to
>disprove "case for substrate heaters is inconclusive". Most of the
>statement you make are false or inconclusive.
I think the people making claims should be the ones coming up with
studies. If you read what I wrote carefully, you will realize that I
did not say that substrate heating is useless. What I wanted to say
was I had not seen much convincing evidence that substrate heating
makes a big difference.
-Shaji
--
----------------------------------------------------------------------------
Shaji Bhaskar bhaskar-at-bnr.ca
BNR, Research Triangle Park, NC 27709, USA (919) 991 7125
by pulliam-at-NREL.ColoState.EDU (Bill Pulliam)
As someone with a background in wetlands Ecology, I can comment on
the hydrology and nutrient cycles in natural wetlands. I have no
first-hand experience witht eh practice of substrate heating,
however
In article <1994Jan31.171620.9822-at-bmers95.bnr.ca> bhaskar-at-brtph181.bnr.ca (Shaji Bhaskar) writes:
>From recent postings on *.aquaria, I get the impression that a lot of
>people have bought into substrate heaters. I've been trying to take
>stock of the situation, and I have a few problems with the concept.
>
>1. The Dupla guys claim that water seeps up slowly through the
>substrate, bringing with it nutrients that the plants need. This is
>what they try to simulate with heating cables. I would think that in
>most rivers (and, in any body of water that is above the water table)
>water flow would be INTO the substrate, not out of it. This water
>would be, I suspect, practically devoid of nutrients.
Contrary to a lot of popular impression, the large majority of water
flowing in to most streams (especially in forested areas) takes place
via groundwater, not surface flow. Thus, water flowing upward through
the substrate is a quite realistic situation for a stream. The
chemistry of this water will be highly variable, with N and P contents
dependent on the nature of the strata it has passed through, the
vegetation and human uses in the uplands, and especially on processes
taking place in the streamside corridor (the riparian zone). This
process is usually very spotty, with highly chanelized flow in some areas.
Water may be either nutrient enriched or nutrient depleted, depending on
how much denitrification, iron-phosphorus coprecipitation, etc. is
taking place. One of the hallmarks of natural wetlands is their
incredible variability, making it very difficult to generalize about their
functions. In larger streams and rivers, the phenomenon of bank storage
is very important. In this case, during high flow water moves
from the stream channel in to riparian groundwater, then returns via
subsurface flow during low flow (water tables in teh midwestern US in the
places that were flooded last year are still elevated and discharging to the
streams). The chemistry of the water that returns is frequently very
different than when it entered the groundwater.
>
>2. Even in stable bodies of water that are level with the water table,
>I would think there is very little inflow of water through the
>substrate. Why would water flow up throughthe substrate? The only
>reason I can think of is evaporation from the lake surface. How does
>the rate of evaporation compare with the flow rates obtained with
>substrate heaters? Is more better? If so, how much more? Does Dupla
>have any valid experimental data to back up their claim?
Again, frequently (but not always) there is substantial sub-surface
flow in to a lake. If the lake has an outlet, then groundwater seepage
can be balanced by outflow. In some cases, there is also subsurface flow
out of lakes. Once again, diversity rules. In trpoical climates, surface
evaporation can run 1 cm/d or so, which is a very small flow rate (turning
over the water in about 6 cm of gravel every 2 days, acconting for
substrate porosity). In a stream or an outflowing lake, flow rates
can be much higher than this, and extremely spottily distributed. In
wetlands on perched water tables (and many artificial reserviors), flow
will be downward in to the substrate.
>
>3. If you use substrate heaters, the gravel is warmer than the water
>above it. This is something that does not occur too often in nature.
>Is this good or bad? In nature, I would expect decreasing temperature
>with depth, and this is not what the heating cables provide.
This is an unnatural situation in most cases, and is the one problem I
have with the concept of substrate heating.
>
>4. What evidence do we have on the net that substrate heaters actually
>work as claimed?
On this topic, you'll have to get answers from someone else.
Hope the brief lesson in wetlands ecology is helpful!
Bill Pulliam
by uweb-at-hpbidrd1.bbn.hp.com (Uwe Behle)
Date: Wed, 2 Feb 1994
Shaji Bhaskar (bhaskar-at-brtph181.bnr.ca) wrote:
: From recent postings on *.aquaria, I get the impression that a lot of
: people have bought into substrate heaters. I've been trying to take
: stock of the situation, and I have a few problems with the concept.
: 1. The Dupla guys claim that water seeps up slowly through the
: substrate, bringing with it nutrients that the plants need. This is
: what they try to simulate with heating cables. I would think that in
: most rivers (and, in any body of water that is above the water table)
: water flow would be INTO the substrate, not out of it. This water
: would be, I suspect, practically devoid of nutrients.
: 2. Even in stable bodies of water that are level with the water table,
: I would think there is very little inflow of water through the
: substrate. Why would water flow up throughthe substrate? The only
: reason I can think of is evaporation from the lake surface. How does
: the rate of evaporation compare with the flow rates obtained with
: substrate heaters? Is more better? If so, how much more? Does Dupla
: have any valid experimental data to back up their claim?
----------------------------------------------------------------------------
The most abundant plant growth occurs in areas of under water springs, which
bring oxygen depleted water with a high concentration of trace elements in
their reductive state to the surface, where they quickly oxydize and become
useless for plants. It is therefore important to generate a slow flow of
water and to have material that can give off trace elements into the
(oxygen depleted) water in the substrate. Nutrients like N,P,K don't play a
role here; even very low concentrations of those in the free water get absorbed
by plants.
----------------------------------------------------------------------------
: 3. If you use substrate heaters, the gravel is warmer than the water
: above it. This is something that does not occur too often in nature.
: Is this good or bad? In nature, I would expect decreasing temperature
: with depth, and this is not what the heating cables provide.
while the gravel may not be warmer than the water, it is definitely not
significantly cooler. Even before substrate heating people have found that
they obtain better results if they keep the gravel warm (by whatever means).
In a normal tank setup the temperature difference between bottom and free water
is several degrees C. This is caused by the heat loss through the bottom and
the fact that cold water is heavier than warm water, so the situation is
self-stabilizing without turbulences.
: 4. What evidence do we have on the net that substrate heaters actually
: work as claimed? George Booth is impressed by them, but he agrees
: that he has no hard evidence to support his subjective evaluation. I
: seem to remember at least one significant difference between his
: Optimum Aquarium setup and his other tanks in addition to substrate
: heaters - the lighting. Jeff Frank (I could be wrong about the first
: name) had posted some articles a long time ago advocating substrate
: heaters. I don't know of any other strong advocates of substrate
: heaters on the net.
Dupla is not the only company advocating substrate heating. The light source
and light colour are definitely not of primary importance as long as the light
level is sufficient. Plants can adapt quite well to a given source of light as
some research done by Philips (a big producer of lighting equipment, among
ther things) has shown.
: All things considered, I think the case for substrate heaters is
: inconclusive. Comments?
Definitely not. Applied correctly they are a big asset to planted tanks.
--
Uwe
NAME Uwe Behle, HP Boeblingen Instruments Division
EMAIL uweb-at-hpbbn.bbn.hp.com (internet), df3du-at-db0sao.ampr.org (packet radio)
by pulliam-at-NREL.ColoState.EDU (Bill Pulliam)
Date: 2 Feb 94
In article <CKLKzG.Jp8-at-hpbbrd.bbn.hp.com> uweb-at-hpbbn.bbn.hp.com writes:
[snip]
>The most abundant plant growth occurs in areas of under water springs, which
>bring oxygen depleted water with a high concentration of trace elements in
>their reductive state to the surface, where they quickly oxydize and become
>useless for plants. It is therefore important to generate a slow flow of
>water and to have material that can give off trace elements into the
>(oxygen depleted) water in the substrate. Nutrients like N,P,K don't play a
>role here; even very low concentrations of those in the free water get absorbed
>by plants.
[snip]
Now this does make sense to me from an ecological/biogeochemical perspective.
If the effect of substrate heating is to increase microbial activity (via
warmer temperatures) and provide for slow water flow (via convection),
that would be very likely to increase the occurence of anaerobic microzones
and provide sources of soluble reduced iron & other redox sensitive elements.
Even a very slow flow UGF wouldn't duplicate this because of the introduction
of large amounts of oxygen. These same processes could also increase P
availability, though the biggest effect is likely to be with Fe. Now I'm
intrigued enough to try one. BTW, oxidized ferric Fe3+ is not useless to
plants, it just requires more energy to find, solubilize, and utilize.
Bill
by uweb-at-hpbidrd1.bbn.hp.com (Uwe Behle)
Date: Wed, 2 Feb 1994
Shaji Bhaskar (bhaskar-at-brtph181.bnr.ca) wrote:
: From recent postings on *.aquaria, I get the impression that a lot of
: people have bought into substrate heaters. I've been trying to take
: stock of the situation, and I have a few problems with the concept.
: 1. The Dupla guys claim that water seeps up slowly through the
: substrate, bringing with it nutrients that the plants need. This is
: what they try to simulate with heating cables. I would think that in
: most rivers (and, in any body of water that is above the water table)
: water flow would be INTO the substrate, not out of it. This water
: would be, I suspect, practically devoid of nutrients.
: 2. Even in stable bodies of water that are level with the water table,
: I would think there is very little inflow of water through the
: substrate. Why would water flow up throughthe substrate? The only
: reason I can think of is evaporation from the lake surface. How does
: the rate of evaporation compare with the flow rates obtained with
: substrate heaters? Is more better? If so, how much more? Does Dupla
: have any valid experimental data to back up their claim?
----------------------------------------------------------------------------
The most abundant plant growth occurs in areas of under water springs, which
bring oxygen depleted water with a high concentration of trace elements in
their reductive state to the surface, where they quickly oxydize and become
useless for plants. It is therefore important to generate a slow flow of
water and to have material that can give off trace elements into the
(oxygen depleted) water in the substrate. Nutrients like N,P,K don't play a
role here; even very low concentrations of those in the free water get
absorbed
by plants.
----------------------------------------------------------------------------
: 3. If you use substrate heaters, the gravel is warmer than the water
: above it. This is something that does not occur too often in nature.
: Is this good or bad? In nature, I would expect decreasing temperature
: with depth, and this is not what the heating cables provide.
while the gravel may not be warmer than the water, it is definitely not
significantly cooler. Even before substrate heating people have found that
they obtain better results if they keep the gravel warm (by whatever means).
In a normal tank setup the temperature difference between bottom and free
water
is several degrees C. This is caused by the heat loss through the bottom and
the fact that cold water is heavier than warm water, so the situation is
self-stabilizing without turbulences.
: 4. What evidence do we have on the net that substrate heaters actually
: work as claimed? George Booth is impressed by them, but he agrees
: that he has no hard evidence to support his subjective evaluation. I
: seem to remember at least one significant difference between his
: Optimum Aquarium setup and his other tanks in addition to substrate
: heaters - the lighting. Jeff Frank (I could be wrong about the first
: name) had posted some articles a long time ago advocating substrate
: heaters. I don't know of any other strong advocates of substrate
: heaters on the net.
Dupla is not the only company advocating substrate heating. The light source
and light colour are definitely not of primary importance as long as the light
level is sufficient. Plants can adapt quite well to a given source of light as
some research done by Philips (a big producer of lighting equipment, among
ther things) has shown.
: All things considered, I think the case for substrate heaters is
: inconclusive. Comments?
Definitely not. Applied correctly they are a big asset to planted tanks.
--
Uwe
NAME Uwe Behle, HP Boeblingen Instruments Division
EMAIL uweb-at-hpbbn.bbn.hp.com (internet), df3du-at-db0sao.ampr.org (packet radio)
by pulliam-at-NREL.ColoState.EDU (Bill Pulliam)
Date: 31 Jan 94
As someone with a background in wetlands Ecology, I can comment on
the hydrology and nutrient cycles in natural wetlands. I have no
first-hand experience witht eh practice of substrate heating,
however
In article <1994Jan31.171620.9822-at-bmers95.bnr.ca> bhaskar-at-brtph181.bnr.ca
(Shaji Bhaskar) writes:
>From recent postings on *.aquaria, I get the impression that a lot of
>people have bought into substrate heaters. I've been trying to take
>stock of the situation, and I have a few problems with the concept.
>
>1. The Dupla guys claim that water seeps up slowly through the
>substrate, bringing with it nutrients that the plants need. This is
>what they try to simulate with heating cables. I would think that in
>most rivers (and, in any body of water that is above the water table)
>water flow would be INTO the substrate, not out of it. This water
>would be, I suspect, practically devoid of nutrients.
Contrary to a lot of popular impression, the large majority of water
flowing in to most streams (especially in forested areas) takes place
via groundwater, not surface flow. Thus, water flowing upward through
the substrate is a quite realistic situation for a stream. The
chemistry of this water will be highly variable, with N and P contents
dependent on the nature of the strata it has passed through, the
vegetation and human uses in the uplands, and especially on processes
taking place in the streamside corridor (the riparian zone). This
process is usually very spotty, with highly chanelized flow in some areas.
Water may be either nutrient enriched or nutrient depleted, depending on
how much denitrification, iron-phosphorus coprecipitation, etc. is
taking place. One of the hallmarks of natural wetlands is their
incredible variability, making it very difficult to generalize about their
functions. In larger streams and rivers, the phenomenon of bank storage
is very important. In this case, during high flow water moves
from the stream channel in to riparian groundwater, then returns via
subsurface flow during low flow (water tables in teh midwestern US in the
places that were flooded last year are still elevated and discharging to the
streams). The chemistry of the water that returns is frequently very
different than when it entered the groundwater.
>
>2. Even in stable bodies of water that are level with the water table,
>I would think there is very little inflow of water through the
>substrate. Why would water flow up throughthe substrate? The only
>reason I can think of is evaporation from the lake surface. How does
>the rate of evaporation compare with the flow rates obtained with
>substrate heaters? Is more better? If so, how much more? Does Dupla
>have any valid experimental data to back up their claim?
Again, frequently (but not always) there is substantial sub-surface
flow in to a lake. If the lake has an outlet, then groundwater seepage
can be balanced by outflow. In some cases, there is also subsurface flow
out of lakes. Once again, diversity rules. In trpoical climates, surface
evaporation can run 1 cm/d or so, which is a very small flow rate (turning
over the water in about 6 cm of gravel every 2 days, acconting for
substrate porosity). In a stream or an outflowing lake, flow rates
can be much higher than this, and extremely spottily distributed. In
wetlands on perched water tables (and many artificial reserviors), flow
will be downward in to the substrate.
>
>3. If you use substrate heaters, the gravel is warmer than the water
>above it. This is something that does not occur too often in nature.
>Is this good or bad? In nature, I would expect decreasing temperature
>with depth, and this is not what the heating cables provide.
This is an unnatural situation in most cases, and is the one problem I
have with the concept of substrate heating.
>
>4. What evidence do we have on the net that substrate heaters actually
>work as claimed?
On this topic, you'll have to get answers from someone else.
Hope the brief lesson in wetlands ecology is helpful!
Bill Pulliam
by booth-at-lvld.hp.com (George Booth)
Date: 12 Dec 1994
Newsgroup: rec.aquaria,alt.aquaria,sci.aquaria
I had a e-mail exchange with a rec.aquaria reader last month that I
think would be of interest in light of the recent spate of "heating
coil" discussions. He had some questions regarding Duplas "10 Golden
Rules" that was posted a while ago. In the exchange below, "> >" is
quoting the Dupla rules, ">" is the reader's question.
> Like I said, I just don't get the rationale [behind the coils]. I
> figured you would be the one to ask.
No problem. I think Dupla has been careful to hide the rationale to
protect their product, i.e., keep it "magic". We didn't see the
rationale at first either and set up a 100g tank without heating coils.
Comparing the 100g tank and a 90g tank we set up with heating coils
led us to hopefully understand more of what's going on.
I think a key concept is that we are NOT trying to mimic what happens
in nature (even though the Dupla description implies that) but we
are trying the achieve an equivalent biological affect. Let me
answer a few of your points first, then comment on what we think is
really going on.
> > 1. The same temperature in the water and in the bed, just as in
> > natural waters. (If the aquarium water is heated up e. g. by means of
> > heating bars, only the water becomes tropically warm, while the bed
> > soil remains at room temperature and the plants notoriously suffer
> > from "cold feet").
>
> In an aquarium the water moves though the gravel fairly freely although
> slowly, at least as quickly as it would in nature, and maybe faster if you
> have UGF.
First of all, without an UGF or RFUGF or the such, I don't think
you'll find much water circulation in the gravel, especially if you
have the smaller size gravel recommended for plants (2-3mm). What
mechanism is there to cause movement? Water won't just move around by
itself; movement needs to powered by some source of energy.
In nature, you have sources of underground water moving to the surface
or surface water moving to aquifers due to natural pressure
differentials. Dupla mentions this in terms of "nutrient springs" in
tropical streams. In our aquariums, there is no such natural
pressures to cause any movement (except for UGF, etc).
> If the water was kept at a constant temp. wouldn't the water,
> which surrounds the gravel particles keep the gravel at that temp also?
The water column will tend to keep the gravel at water temperature
through conductive heating; heat will "seep" downward. However, in
glass tanks especially, the glass bottom is radiating heat into the
room, cabinet, etc, unless insulation is provided. This will tend to
keep the roots cooler than the water temperature. Even with
insulation, I think you'll find the bottom of the substrate cooler
than the top, just not as much.
> What's warming the substrate in the tropics? The warmth doesn't come from
> the earth, it comes from the sun. The sun warms the water, the substrate
> doesn't. The top of the water is always warmer than the bottom even in
> relatively shallow water.
Underground springs may bring up volcanic warmth (there are things
like "hot springs" everywhere). Also, if the bottom is dark (old
leaves, dark soil, whatever), it will pick up more heat from the sun
than the relatively clear water would. I don't know how significant
this would be (especially in a deep jungle) but in open streams it
may be important.
> > 2. Bed water currents which prevail in natural waters are copied;
> > nutrients are fed to the roots, the materials discharged by the roots
> > are carried away.
>
> OK, I understand that the warm water rises carrying with it the wastes
> (assuming roots discharge materials that need to by carried away) and is
> replaced by the cooler water carrying nutrients from above (oops, aren't
> you cooling the roots to the temp of the water above?). Is this copying
> nature? Warm water doesn't rise from the gravel, does it? Whats down there
> warming it up? In nature the warm water is already on top being heated by
> the sun. The best you could hope for it seems is a turbulent stream in
> which the water is evenly mixed, but I don't think most of our plants come
> from conditions like that.
Actually, a lot of the plants do come from fast moving streams,
especially plants from SE Asia like crypts.
Again, we're not trying to copy nature, just achieve the same effect.
Here is a list of substrate processes I think are important (no
particular order of importance implied):
1) Provide warmth in the substrate for certain plant species (Barclaya
longifolia, specifically). In this case the substrate should be
warmer than the water.
2) Provide warmth in the substrate to speed up biochemical processes.
3) Transport nutrients from the water into the substrate. Important
nutrients would be ammonium (fish waste, etc), iron (from trace
element additions), calcium, potassium and other trace elements.
This will replenish nutrients used by the roots and provide long
term viability (in terms of years).
4) Transport harmful products out of the substrate. Decomposition
products may be harmful to plant roots. There is also conjecture
that plants give of low level toxins to keep other plants out of
their territory (successful weeds have made this an art form).
If these toxins build up due to poor circulation, the plant may
harm itself.
5) Provide a chelating medium that binds the divalent state of trace
elements with an organic molecule, enabling the trace element to
be adsorbed by root hairs.
6) Provide a reducing rather than oxidizing environment so that trace
elements are kept in their divalent state (usable by plants) or
are reduced from their oxidized trivalent state. Iron especially
will rapidly oxidize in water with normal levels of oxygen.
Heating coils provide items 1 and 2 directly. The convection currents
generated by the "spot" heat source of the coils provide for 3 and 4.
Laterite in the bottom 1/3 of the substrate provides for 5. The slow
convection currents, coupled with nitrifying bacteria in the gravel
will reduce the concentration of oxygen getting to the bottom layer
of the gravel, providing 6.
A heating pad under the tank will tend to warm the entire bottom layer
uniformally. This will provide 1 and 2 but I suspect the heat will
go through the gravel as conduction and won't generate convention
currents. Thermodynamics theory says that conduction will occur up to
a certain heat threshold and then convection currents will be formed with
more heat. I think the linear hot zones generated by proper spacing
of the coils along with the higher temperatures of the coils will
provide this. Yes, there will be hot and cool zones for the roots
but I think the other factors outweight this.
Schemes that use warm water flowing in tubes in the gravel (Bioplast,
for example) won't work, IMHO, because they can't generate enough
heat. Bioplast wraps some tubing around a heater and pipes it through
the gravel with a pump. The first foot or so of the tubing may get
hot enough (though I doubt it) but the water in the coil will cool off
rather quickly as it travels through the tube. If the tube is
insulated enough to keep the water hot, then it won't transfer any
heat to the gravel.
> If you truly need to keep you roots warm and want water flowing up through
> the gravel why don't you just surface skim your water and return it though
> a reverse flow UGF?
This will provide for 2 and 4 and perhaps 6. It may provide for 1 if
you heat the water before putting it through the RUGF. 3 is kind of
hard since the water is usually filtered before going to the RUGF (to
avoid injecting crud into the gravel) and trace elements probably will
be oxidized in the filter (oxidizing is a bio-filter's purpose). 5 is
a problem because a RUGF will probably push the laterite up and out of
the gravel. Don't get me wrong, a RUGF *may* provide the 6 processes,
but it would be difficult to get it set up with the right flows and
even flow across the substrate and proper mechanical filtering, etc.
A coil setup is a "no-brainer" if you have the correct wattage.
UGF will provide 2, 3 and 4. 1 would be very tricky to achieve, if
not impossible. Detritus pulled into the gravel can provide 5 but
6 is almost impossible unless a very slow flow is used and that
would be hard to do evenly across the whole substrate.
We have three ~100g tanks with coils and one 85g tank with UGF.
All grow plants equally well but the 85g is much more unstable.
We think it is sensitive to too much detritus building up in
the gravel; a thorough vacuuming every 6-9 months perks it up.
The coil tanks require no gravel vacuuming and the 90g tank was
rock solid biologically for at least three years. We replanted
at that point because some of the plants had gotten out of control
but we didn't "tear down" the tank - just replanted.
I think this is the key to the cables - long term stability. Plants
will grow fine without them if you can accomplish most of the six
things I mentioned. Just pulling up plants for trimming every
month will accomplish as lot (stirring up the gravel, moving
roots out of their toxin zone, etc).
-----------------------------------------------------------------------------
George Booth "Nothing in the world is more dangerous
booth-at-hplvec.lvld.hp.com than sincere ignorance and conscientious
Freshwater Plant Tank Technology stupidity" - Martin Luther King, Jr.
-----------------------------------------------------------------------------
by "Thomas Barr" <tcbiii/earthlink.net>
Date: Wed, 15 Mar 2000
I was pondering the nature of the RFUG systems I am so endeared too.
Hydroponic growing is the same (aerobic substrates) and Tropica/Horizon
Growers use this to grow their plants.
Now if the most respected growers are using this, why aren't more using this
system basing it on a submersed set up? CO2 and light are not considered. We
add this and there is not much problem for the growers in this area. so if
we are doing a good job with light and CO2 what's left? Nutrients and soil
but also O2. There's plenty for respiration in air but what about in a tank?
If things are going well there should be plenty right? I had 120% at the end
of a photo period when a saltwater friend dragged over a DO meter. In the
morning it measured 90% or so. I don't think .....but I could be wrong
.........that this might be an issue. All that's left is nutrients and soil.
Many of my tanks have the spray bar at the back bottom blowing the filtered
CO2 rich water across the bottom of the tank to the front and/or RFUG's at
least. Seems to me that this is a key factor(aerobic substrates). Comments?
Regards,
Tom Barr
by "Roger S. Miller" <rgrmill/rt66.com>
Date: Fri, 7 Jul 2000
Folks,
George was talking about circulation rates induced by heating coils. I
wondered about the circulation rates that would apply *without*
convection, and estimated for one of my tanks that the water in the
substrate might turn over about every 6 weeks or so. Details follow.
Karen Randall once commented that plants by themselves would induce
circulation in the substrate. Her idea was based on some research
summarized in an article by Ole Pedersen at the Tropica web site.
Briefly, the idea is that aquatic plants actively transport water from
their roots to their shoots and into the water column. Water pumped out
of the substrate is replaced by water moving down through the substrate
from the water column. Thus there is a continuous circulation of water
through the substrate.
I went looking for the original research by Pedersen and Kaj Sand-Jensen
so that I could get a sense of how much water the plants might move. The
article (complete reference at the end of this letter) makes for
interesting reading.
The authors measured flow rates induced by several species of cold water
plants. From the range of values they report, a rough mid-range estimate
of the flow rate would be about 0.1 cc of water per gram plant dry weight
per hour. This varies from species to species and (inferring from their
discussion) may also vary with the plant growth rate and a few other
parameters.
It's a little tough to apply that to an aquarium. I have to admit that I
have never ripped all the plants out of a tank, reduced them to ash and
determined their dry weight. Just the same, it seems like it might be
estimated. I'll use my 55 gallon tank as an example. I'll guess that it
contains about 3 lbs of plants. If the plants are 95% water (ball park
guess) then the tank contains 0.15 lbs or about 68 grams of plant dry
weight.
68 grams of plant dry weight then could induce a flow of 6.8 cc of water
per hour. The substrate has an area of 3774 square cm, of which about 25%
(944 square cm) would be open for water movement. The flow rate through
the substrate would be 6.8 cc/hour divided by 944 square cm -- a
remarkably small 0.0072 cm per hour, or 0.17 cm per day. The substrate is
about 7.5 cm thick, so it would take about 44 days, or about 6 weeks, for
the plants to turn over the whole volume of water in the substrate.
In reality the substrate would contain some stagnant areas and other areas
where the flow is concentrated. Also, the downward flow rate at any depth
in the substrate would depend on how much root mass there is below that
depth, so there would be more turnover near the top of the substrate then
at the bottom.
At those slow rates the diffusion rates and stirring work done by
burrowing critters are probably significant factors.
Roger Miller
The reference is:
Perdersen, Ole and Kaj Sand-Jensen, 1993. Water transport in submerged
macrophytes. Aquatic Botany, v 44, pp 385-406.
No time to reach a library? If you have a fax, a credit card and internet
access to Uncover or some similar library service then you can have the
article faxed to you.
by "Roger S. Miller" <rgrmill/rt66.com>
Date: Wed, 03 Jan 2001
Tom Barr wrote:
> Claus of Tropica mentioned that they tested one tank for optimum flow rates
> in the substrate and came out with a figure of .49 liters/m^2/day. Not much.
> Osmosis ain't far behind that.
That's an interesting value.
Ole Pedersen and Kaj Sand-Jensen (Aquatic Botany 44(1993) p 385-406)
measured the rate of transport of water from the substrate to the water
column generated by several different submersed plant species. In an
aquarium, water transported upward by the plants will cause an equal
amount of water to be drawn from the water column down into the
substrate -- that is, it will cause substrate circulation. Karen
Randall pointed that out to this group some time ago.
Pedersen and San-Jensen's results cover the range from 7 to 143
microliters per gram plant dry weight per hour. I'll use a mid-range
value of 70 microliters/gr/hr for a little calculation.
I think my 55 gallon tank (0.4 square meters floor area) contains
something like a kilogram of plant wet weight. It's reasonable to
estimate that the plants are about 95% water (about 5% dry weight) so
the tank would contain about 50 grams of dry plant mass. That dry
weight of plants would circulate about 3500 microliters of water per
hour, of 3.5 milliliters/hour. Spread out of the 0.4 square meter tank
area that comes out to 8.75 milliliters/square meter/hour, or 0.21
liters/square meter/day.
Gee. Without any further finagling, that's already at 43% of Claus'
optimum circulation rate.
Petersen and San-Jensen argued that the water transport rate should
increase with growth rate. They ran their tests in cold water (12
degrees C, 54 degrees F), with CO2 at atmospheric equilibrium levels and
with lighting that was low (90 micromole/sq meter/sec) compared to what
we are often keep in our tanks (for comparison, I'd estimate from Ivo
Busko's data at Aquabotanic.com that my 55 gallon tank with 160 watts of
NO fluorescent lights is lit with 200 micromoles/sq. meter/sec). I can
easily envision that the growth rates in my tank (and by extension,
probably in the typical CO2-augmented, well-lit plant tank) are
considerably higher than they were in the Pedersen and San-Jensen
experiments; if so then perhaps that 0.21 liters/square meter/day
estimate should be taken as a *minimum* value for a planted tank.
The possibility that plant-induced circulation rates can be quite a bit
higher than this estimate is further reinforced by values that Pedersen
and San-Jensen site in their literature review where (for instance) one
submersed, 20 cm Nomaphila scricta was found to "pump" 2.1 ml/hour.
The uncertainties in these estimates are so large that the results can't
be used for much. Just look at how the results change if the plants are
97% water instead of 95% water! Despite that, I think they are
sufficient to demonstrate that plants can provide substrate circulation
without any additional intervention by the aquarist.
Roger Miller
The Krib
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