Substrate Comparison Thread
Contents:
- clay, laterite, kitty litter/vermiculite and soil
by Stephen Pushak <teban/powersonic.bc.ca> (Sun, 28 Dec 1997)
- clay, laterite, et al
by George Booth <booth/hpmtlgb1.lvld.hp.com> (Mon, 29 Dec 1997)
- Laterite, kitty litter, et al
by "Roger S. Miller" <rgrmill/rt66.com> (Mon, 29 Dec 1997)
- Black spots on Microsorum
by eworobe/cc.UManitoba.CA (Mon, 29 Dec 1997)
- laterite, kitty litter, clay
by Stephen Pushak <teban/powersonic.bc.ca> (Mon, 29 Dec 1997)
- iron content of soils
by Stephen Pushak <teban/powersonic.bc.ca> (Tue, 30 Dec 1997)
- Substrates
by George Booth <booth/hpmtlgb1.lvld.hp.com> (Tue, 30 Dec 1997)
- laterite, et al
by George Booth <booth/hpmtlgb1.lvld.hp.com> (Tue, 30 Dec 1997)
- Dueling substrates
by George Booth <booth/hpmtlgb1.lvld.hp.com> (Wed, 31 Dec 1997)
- Laterite
by krandall/world.std.com (Sat, 03 Jan 1998)
by Stephen Pushak <teban/powersonic.bc.ca>
Date: Sun, 28 Dec 1997
We should avoid confusing the properties of laterite with the various
clays and other soils. Laterite is quite different, it is chiefly
composed of iron and aluminum oxides/hydroxides. In comparison to
ordinary soil (with a clay & humus component), or any of the various
fine textured clays, laterite has a relatively low CEC (cation exchange
capacity = the ability to adsorb positively charged nutrient ions).
Improving the CEC of your substrate is quite easy; vermiculite or other
expanding layer clays (like kitty litter) are just one option for this.
Fine textured clays or soils with a low organic content are another way.
Humus has a very high CEC and is also be able to adsorb negatively
charged ions (anions). 1 to 5 percent humic material in a substrate is
optimal. Refer to my homepage for a long and technical discussion of
substrate materials (Substrates for aquatic plants under Articles)
http://home.infinet.net/teban/index.html
Dave Huebert made the following comments in an email discussion last
summer:
"In a landmark paper published in Science 207: 987 to 989 (1980)
two Canadians by the name of Carrignan and Kalff clearly demsonstrated
that rooted aquatic plants will absorb the majority of P from the
sediment EVEN UNDER HYPEREUTROPHIC CONDITIONS! This was the first paper
which unambiguously showed the preference of aquatic plants for
sedimentary P. Nitrogen studies are somewhat less clear, mainly because
N is so difficult to work with. Nichols and Keeney, Fresh.Biol.6:145 to
154 were perhaps the first to indicate that rooted aquatic plants
acquire the majority of N from the sediment. After that was an excellent
study by Barko and Smart. They turned the question around somewhat and
asked "which nutrients can be left out of the water". Their results
clearly showed that N was not needed in the water column for optimal
growth. I asked the same type of question in a paper published in 1982
and came up with the same result (Huebert and Gorham (Aquatic Bot. 16:
269 to 283). These experiments, and several others, indicated that with
a fertile substrate the only nutrients required in the water column are
Ca, Mg, K and of course CO2 (I must admit, though, that the evidence for
micronutrients is scant and it is in fact likely that water column
additions of micronutrients is a good strategy ... though my swords and
Sagittaria are completely indifferent to whether or not I add
micronutrients) Little work has been done since the mid eighties since
the dozen or so published studies were fairly clear in their results and
there is not much money for this type of research (its also difficult
and time consuming).
"On the other side of the coin, there have been a plethora of
studies which indicate clearly that rooted aquatic plants will not grow
optimally on a sand or other infertile substrate no matter how richly
you fertilize the water column (perhaps the earliest is by Pond, 1905)"
Laterite certainly provides a certain amount of useable iron in the
substrate. Substrates with very low organic content do not have a low
enough redox potential to provide a continuous supply of substrate iron
and these kinds of aquariums will benefit from carefully controlled
doses of chelated iron in the water. We've also found that the addition
of peat to a soil substrate keeps the redox potential low enough to
provide sufficient iron to maintain moderate growth rates without
resorting to chelated iron dosing. It's probably not wise to combine
really high light levels with significant amounts of chelated iron in
solution as this seems to promote many types of algal growth especially
filamentous algae. NOTE: for these reasons, we do NOT RECOMMEND that you
try a mix and match approach but stick with a single, proven approach.
Quoting Karen Randall:
"I think the strongest merit of laterite is safety. In the hands of
a novice, even _good_ soil can be a mess. Even in the hands of a more
experienced aquatic gardener the _wrong_ soil can be a disaster, and
there is no way to know until you've tried a particular soil how you'll
do with it. TOA approach, and I must say, the one I try to follow in
talking to beginning aquatic gardeners is to help them be successful the
_first_ time. Once the hook is "set"<g> there's plenty of time for
experimentation and improvement. But if they are faced with massive
problems in the first round, they are likely to give up in disgust."
I hope that we can describe some procedures to safely use natural soils
which are also suitable for novices but it should be noted that
following the procedures is more critical.
As Dave Huebert points out above, rooted aquatic plants do best when
they can get an adequate supply of phosphorus from the substrate.
Laterite and other iron compounds in a substrate help to sequester
phosphates. Clays, kitty litter and vermiculite are not able to do this.
Natural, amorphous soils commonly contain significant amounts of iron
(typically 5% according to Diana Walstad). The amount of phosphates in a
soil is extremely variable and for this reason, soils with large amounts
of freshly composted material should be avoided since they readily
release these phosphates into your aquarium water. On the other hand, an
appropriate amount of organic material or phosphates can give your
plants a tremendous boost.
Roger Miller had asked recently about his Cryptocoryne balansae
(reclassified as C crispatula) which only seemed able to support 2 or 3
leaves at a time. Roger, I presume that you are ensuring an adequate
supply of nitrogen in solution and I recall that you had mentioned plans
to experiment with some phosphate fertilization in your substrate. I
wonder if this Crypt melting is really a symptom of a shortage of
phosphorus and a natural reaction of the plant by "recycling" phosphates
from older leaves.
In my 75 gallon tank, I had very good growth of C balansae for several
months without loss of older leaves but more recently the older leaves
have begun to melt and are replaced by new leaves. The substrate in this
tank contains a lower organic material content and much of this is from
peat which is a very poor source of phosphates. I suspect that I am also
beginning to have reduced levels of phosphates. Another plant which has
shown a reduction in growth rates in this tank is Aponogeton crispus.
The fish load in this tank is very low.
Roger, have you tried adding any form of phosphate fertilizer into the
substrate? Probably the best way would be to use something like enriched
clay balls or Jobe's plant sticks which are made from a material
designed to slow the release of the nutrients. I don't think the plastic
coating on Osmocote pellets does an adequate job of this and prefer to
use these inside iron rich clay balls. I'll probably put some of these
into my 75 gal shortly.
Steve
by George Booth <booth/hpmtlgb1.lvld.hp.com>
Date: Mon, 29 Dec 1997
> Date: Sun, 28 Dec 1997 23:04:40 -0800
> From: Stephen Pushak <teban-at-powersonic.bc.ca>
I'm afraid I must take issue with this posting. Much of this comes across as
fact when, in actuality, it is conjecture. I have no problem with anyone
posting conjecture as such, but I do not want to see this passed of as what
sounds like scientific evidence. The author has shown by his own results that he
does not yet hold the "key" to the perfect substrate (or even one that works
well in the long run). I would much prefer see a few "in my humble opinion" and
"I think" scattered appropriately throughout claims such as these.
> In comparison to
> ordinary soil (with a clay & humus component), or any of the various
> fine textured clays, laterite has a relatively low CEC (cation exchange
> capacity = the ability to adsorb positively charged nutrient ions).
> Improving the CEC of your substrate is quite easy; vermiculite or other
> expanding layer clays (like kitty litter) are just one option for this.
What is the proper level of CEC in the substrate? Do different plants do better
with more CEC than others? Which plants are sensitive to "not enough" CEC? How
do you measure how much CEC you already have? Why would one want to
gratuitously "improve" the CEC if there already is enough? What are the
consequences of having too much CEC? Does a larger amount of a safe but low CEC
material such as laterite produce the same results as a smaller amount of more
dangerous but higher CEC material? If laterite has such an abysmal CEC, why
does it work so well?
> 1 to 5 percent humic material in a substrate is optimal. Refer to my homepage
> for a long and technical discussion of substrate materials
I read your long discussion (three times!) and did not see how "1 to 5 percent
humic material" was found to be optimal. Do you have a reference? Is this by
weight or volume? I have 200 pounds of gravel. Does this mean I need 2 to 10
pounds of humic material? Given the nature of humic material, that sounds like
a HUGE amount of crud to add to the tank.
> Dave Huebert made the following comments in an email discussion last
> summer:
> ...
> "On the other side of the coin, there have been a plethora of
> studies which indicate clearly that rooted aquatic plants will not grow
> optimally on a sand or other infertile substrate no matter how richly
> you fertilize the water column (perhaps the earliest is by Pond, 1905)"
This doesn't jive with my experiences with massive plant growth using plain
gravel substrates, undergravel filters and Dupla fertilizers. Just what is the
scientific definition of "optimal"? I hope it's more complicated than growth
rates. Perhaps the researchers performing the plethora of studies just didn't
know how to grow plants! For example, most of the aquatic plant "bibles"
published prior to 1980 (Rataj and Horeman is a shining example) clearly show
that the authors were rather clumsy at their approaches to growing plants.
References to maximum height and propagation characteristics indicate that their
husbandry was marginal to say the least.
> Laterite certainly provides a certain amount of useable iron in the
> substrate. Substrates with very low organic content do not have a low
> enough redox potential to provide a continuous supply of substrate iron
Are you saying that laterite does or does not continuously supply iron (since
you include it in the category of low organic content)? Do you have some
reference for this? How does the redox potential of a laterite based substrate
differ from an organic substrate? What redox levels are needed to produce a
continuous supply of iron? How do you measure these levels (and I mean "you"
personally, since you claim to have so much experience in this area)? How do you
know if plants aren't receiving enough iron from the substrate?
> We've also found that the addition
> of peat to a soil substrate keeps the redox potential low enough to
> provide sufficient iron to maintain moderate growth rates without
> resorting to chelated iron dosing.
How have "we" found this out? I have seen nothing you have posted that gives
credence to this assertion. Have you measured the redox potentials before and
after? How much peat do you have to add to how much substrate? What else is in
ths substrate? How does iron get there in the first place? Is this state
sustainable for more than a few months?
I think you are making this up. I challenge you to prove this statement or
retract it.
> It's probably not wise to combine
> really high light levels with significant amounts of chelated iron in
> solution as this seems to promote many types of algal growth especially
> filamentous algae.
Perhaps it is not wise for YOU to do this. It works just fine for me and others
who have tried it and does NOT promote filamentous algae growth.
> I hope that we can describe some procedures to safely use natural soils
> which are also suitable for novices but it should be noted that
> following the procedures is more critical.
And just who is this "we" that you refer to? If you are presuming to speak for
the collective APD, you are very misguided. If you are presuming to speak for
the AGA, you are way off base. If you are speaking for yourself and a few
others, state exactly WHO is giving this advice.
> In my 75 gallon tank, I had very good growth of C balansae for several
> months without loss of older leaves but more recently the older leaves
> have begun to melt and are replaced by new leaves. The substrate in this
> tank contains a lower organic material content and much of this is from
> peat which is a very poor source of phosphates. I suspect that I am also
> beginning to have reduced levels of phosphates. Another plant which has
> shown a reduction in growth rates in this tank is Aponogeton crispus.
> The fish load in this tank is very low.
Let us know when you find a substrate recipe that works for more than a few
months. Then you can be the self-proclaimed King of Substrates and I will not
have to get all excited when you post your substrate idea du jour. Until then,
and as long as I don't have a stroke reading this stuff, I will continue to take
issue with pompous postings like this.
Sincerely,
George "should have taken vacation over the holiday break"
by "Roger S. Miller" <rgrmill/rt66.com>
Date: Mon, 29 Dec 1997
Thanks, Steve for this post. The quotes from Dr. Dave and from Karen
Randall are great. I'd like to expand (gasp!) on one point.
> We should avoid confusing the properties of laterite with the various
> clays and other soils. Laterite is quite different, it is chiefly
> composed of iron and aluminum oxides/hydroxides. In comparison to
> ordinary soil (with a clay & humus component), or any of the various
> fine textured clays, laterite has a relatively low CEC (cation exchange
> capacity = the ability to adsorb positively charged nutrient ions)...
This is correct. CEC is very important to the distribution of Ca++, Mg++,
Na+, K+ and NH4+ between soils and water, but there is also a second
factor called surface adsorption, which is independent of the ionic
charge. This is a tendency for solutes to become attached to the surfaces
of particles in the soils or sediments. Surface adsorption is measured
with a value called the "distribution coefficient" (Kd). Freshly
precipitated metal hydroxides provide very high Kd values, and phosphates
have a particularly high affinity for being adsorbed.
> As Dave Huebert points out above, rooted aquatic plants do best when
> they can get an adequate supply of phosphorus from the substrate.
> Laterite and other iron compounds in a substrate help to sequester
> phosphates. Clays, kitty litter and vermiculite are not able to do this.
> Natural, amorphous soils commonly contain significant amounts of iron
> (typically 5% according to Diana Walstad).
Well, actually pretty much all materials (including glass beads) have some
capacity from surface adsorbtion, but there is a big variation in the
distribution coefficient for different materials and solutes. The biggest
variable seems to be the amount of surface area provided by the sediment.
Fine-grained sediments of all types - especially clays - can have
significant capacities for adsorbing solutes because they provide a large
surface area.
Metal hydroxides are very good adsorbers for inorganic solutes - in fact
I've read the argument that high adsorbtion coefficients measured on clays
are actually caused by a thin film of hydroxides on the surface of the
clay. But the Kd value for hydroxides apparently drops off as the
sediment "matures" - perhaps because the surface adsorbtion sites are
already occupied but more likely because the hydroxide particulates are
very "fluffy" when they're new but consolidate over time and lose much of
their surface area. As a result it isn't a given that laterite will have
a much higher surface adsorbtion capacity than a clay soil, because the
iron and aluminum hydroxides in laterite are probably going to be very
well aged.
I guess my point is that you should be able to get a good substrate with
clay or with laterite. Either one provides the ability to hold
phosphorus, though laterite might hold more. Clays (and maybe kitty
litter) would have a better capability to hold ammonium. Also in either
case the nutrients in the soil can become depleted over time and you have
to arrange some means of replacing the nutrients that the plants have
taken out.
Organic particles in sediments are very effective adsorbers for organic
solutes - particularly those that aren't very soluble in water. I haven't
read of natural soil organics being very significant adsorbers of
inorganic solutes. They do provide CEC and may chelate some solutes, but
those are different reactions.
> Roger, have you tried adding any form of phosphate fertilizer into the
> substrate? Probably the best way would be to use something like enriched
> clay balls or Jobe's plant sticks which are made from a material
> designed to slow the release of the nutrients. I don't think the plastic
> coating on Osmocote pellets does an adequate job of this and prefer to
> use these inside iron rich clay balls. I'll probably put some of these
> into my 75 gal shortly.
>
I haven't tried this yet, but it gives me a good angle to persue. Thanks.
Roger Miller
by eworobe/cc.UManitoba.CA
Date: Mon, 29 Dec 1997
George;
These are the holidays! Chill
Whenever I quote a study or scientific results the information was
collected in a sound manner... by that I mean adequate controls,
satistical analyses and above all, healthy plants. For instance, I spent
a year, seven days a week, 8 to 12 hours a day learning how to grow Lemna
trisulca BEFORE I started my growth experiments... this is not unusual.
The best experimenters typically use 'weed' species (thats where the
funding is) and will have their plants doubling every two to four days
during experiments. In experiments where HEALTHY plants have been grown
side by side with and without a fertile substrate, the plants in sand
have always grown statistically less than the plants in soil... even in
the presence of an enriched water column. If you want references, read
John Barkos stuff... hes American and probably THE reference on the
mineral nutrition of aquatic plants.
Happy holidays
dave.
by Stephen Pushak <teban/powersonic.bc.ca>
Date: Mon, 29 Dec 1997
Dave Gomberg takes issue with the statement:
> >Natural, amorphous soils commonly contain significant amounts of iron
> >(typically 5%
Thanks for the correction Dave. I rechecked my reference and it should
have been 0.4% not 5%. My error. :%]
George Booth writes:
> The author has shown by his own results that he
> does not yet hold the "key" to the perfect substrate (or even one that works
> well in the long run).
Actually, most people find that I grow quite nice aquatic plants. Let
the readers judge for themselves; my website is
http://home.infinet.net/teban/index.html I never said I had the key to
the perfect substrate. In fact I will state (again) that there is no
such thing as a perfect substrate. If you read my substrate article you
will find that I state that there are many factors to consider in making
an appropriate choice of substrate materials.
> What is the proper level of CEC in the substrate?
There is no such thing as a proper level of CEC. It is well understood
that soils with a higher CEC value are better able to retain nutrients.
There is a table of CEC values for various substances in my
substrate article. Please note that laterite also has a CEC value. One
of the major points of my post was that laterite and kitty litter are
quite different in their characteristics.
> Do different plants do better
> with more CEC than others? Which plants are sensitive to "not enough" CEC? How
> do you measure how much CEC you already have?
I have never heard of specific plants requiring a specific CEC value.
I'm not familiar with the laboratory techniques for measuring CEC and I
don't think we should mislead people into thinking there is any value in
attempting to measure it.
> If laterite has such an abysmal CEC, why
> does it work so well?
I don't believe that the CEC of laterite is it's key advantage. You are
pretty quick to criticize empirical results as non-scientific but we
should remember that the only evidence we have about laterite is
empirical. We can only surmise that laterite and other substances help
to bind phosphates in the substrate.
> > 1 to 5 percent humic material in a substrate is optimal. Refer to my homepage
> > for a long and technical discussion of substrate materials
>
> I read your long discussion (three times!) and did not see how "1 to 5 percent
> humic material" was found to be optimal. Do you have a reference?
Yes, experiments by Barko and Smart clearly indicate that sediments with
higher than 5% organic content actually inhibit growth. Sediments with
lower than 5% organic content grew plants better as the organic content
increased. Barko and Smart theorized that this is due to the correlation
of fertility and organic material. My substrate article should include a
reference section.
> Is this by weight or volume?
By weight.
> I have 200 pounds of gravel. Does this mean I need 2 to 10
> pounds of humic material?
No. Your layer of gravel is probably too deep for that. I would suggest
that it would be more appropriate to use a layered approach similar to
what is advocated for laterite. I wouldn't suggest adding humic material
to gravel anyhow. It would be better to choose a loamy soil with
approximately these values. I don't think the precise value is critical.
> > Dave Huebert made the following comments in an email discussion last
> > summer:
> > ...
> > "On the other side of the coin, there have been a plethora of
> > studies which indicate clearly that rooted aquatic plants will not grow
> > optimally on a sand or other infertile substrate no matter how richly
> > you fertilize the water column (perhaps the earliest is by Pond, 1905)"
>
> This doesn't jive with my experiences with massive plant growth using plain
> gravel substrates, undergravel filters and Dupla fertilizers.
You are assuming that your Dupla substrates are infertile. If your
substrate helps to grow better aquatic plants, it can only be because it
is fertile. Any other theories?
> > We've also found that the addition
> > of peat to a soil substrate keeps the redox potential low enough to
> > provide sufficient iron to maintain moderate growth rates without
> > resorting to chelated iron dosing.
>
> How have "we" found this out?
In this case I am referring to Paul Krombholz. I have duplicated this
with my most recent tank however I cannot make any long term
observations at this time. At present I have not added any chelated iron
to my 49 gallon tank for several months. Growth rates are good and on
those occassions when I did make chelated iron additions, there was no
perceivable increase in growth rates except for green spot algae which
flourished.
> > It's probably not wise to combine
> > really high light levels with significant amounts of chelated iron in
> > solution as this seems to promote many types of algal growth especially
> > filamentous algae.
I will qualify really high lighting to mean 4+ wpg or partial sunlight
and significant chelated iron to be greater than 0.2 ppm. I stand by my
statement. I just want people to be aware that higher light intensities
may mean making adjustments. If your aquarium is in the range of 1-2
wpg, then you probably won't need the high quality iron test kit that
George needs. ;-)
> Let us know when you find a substrate recipe that works for more
> than a few months.
I have George. Since when did we make a rule that says you're not
allowed to periodically fertilize the substrate?
Roger S. Miller wrote:
>> Metal hydroxides are very good adsorbers for inorganic solutes - in fact I've read the
argument that high adsorbtion coefficients measured on clays are actually caused by a thin
film of hydroxides on the surface of the clay. But the Kd value for hydro
xides apparently drops off as the sediment "matures" - perhaps because the surface adsorbtion
sites are already occupied but more likely because the hydroxide particulates are very
"fluffy" when they're new but consolidate over time and lose much of their
surface area. As a result it isn't a given that laterite will have a much higher surface
adsorbtion capacity than a clay soil, because the iron and aluminum hydroxides in laterite are
probably going to be very well aged. <<
How could these be "renewed"? Is there another way to achieve the same
effect? This sounds like a very interesting area for further discussion.
>> I guess my point is that you should be able to get a good substrate with clay or with
laterite.<<
Yup. But I want to stress that the properties of the many various types
of clays and lateritic soils are quite diverse. That was my central
point.
>> Either one provides the ability to hold phosphorus, though laterite might hold more. Clays
(and maybe kitty litter) would have a better capability to hold ammonium. Also in either case
the nutrients in the soil can become depleted over time and you h
ave to arrange some means of replacing the nutrients that the plants have taken out. <<
Yes, I sure don't see any problem with periodically adding some
nutrients to the substrate when we get an indication from the plants.
Sometimes we may want to maintain slow growth and sometimes we may want
to increase it as you probably want to do with your C balansae. In my
case, my plant is already quite large with a large number of leaves so I
haven't felt that its critical to fertilize yet. I suppose it bears
mentioning that I also advocate watching your plants to observe when it
is time to make changes, just as Karen has said repeatedly.
Thanks for the new insights on other adsorption characteristics Roger.
I'd be very interested to learn more about metal hydroxide binding of
phosphates and the other things you mention.
Steve
by Stephen Pushak <teban/powersonic.bc.ca>
Date: Tue, 30 Dec 1997
Dave Gomberg's comment prompted me to triple-check my references on the
iron content of soils. My numbers come from an article in TAG vol 6:4 in
by Diana Walstad entitled "Iron: The Limiting Nutrient for Algae?". She
said:
"Iron, silicates and aluminum are the major components of mineral
soils, with iron the fourth most abundatn element in the earth's crust.
(Bowen, Brand). The total iron content varies from 1 mg/g soil in some
leached sands to over 3000 mg/g in some tropical soils such as laterite
(Wild). Median values for iron for all soils and sediments are reported
to be 40 and 41 mg/g, repectively (Bowen). The amount of iron in all of
these soils and sediments is more than adequate to meet the nutrient
requirements of aquatic plants. Indeed, I calculated that if I were to
use ordinary soil containing median levels of iron (40 mg/g) for an
underlayer in one of my aquariums, there would be enough iron for my
plants for 33,000 years."
The references quoted:
Bowen HJM. 1979. Environmental Chemistry of the Elements. Academic Press
(New York)
Brand LE, Sunda WG and Guillard RRL. 1983. "Limitation of marine
phytoplankton reproductive rates by zinc, manganese and iron". Limnology
and Oceanolography 28:1182-1198.
Diana Walstad had some other excellent points to make in this article.
For example, in nature, algae growth is limited by P however in the
aquarium we typically have P concentrations 100 times or more that found
in unpolluted freshwater. There is strong evidence that the limiting
factors for algae growth in aquariums are typically light intensity and
available iron in the water. Repeatedly in the APD it has been stressed
that it is critical to maintain 0.1 ppm (or less) chelated iron in the
water to avoid algae problems in well lit aquariums.
My motivation for discussing and researching alternatives to The Optimum
Aquarium method designed for informed aquatic gardeners:
1) to reduce our reliance upon expensive, commercial products such as
test kits, laterite and fertilizers.
2) to shed light on the properties which make substrates (including
laterite substrates) work.
Steve
by George Booth <booth/hpmtlgb1.lvld.hp.com>
Date: Tue, 30 Dec 1997
>Date: Mon, 29 Dec 1997 16:35:49 -0600 (CST)
>From: eworobe-at-cc.UManitoba.CA
>
>These are the holidays! Chill
If you mean by "chill" that I should ignore what I believe is misleading
information just because it's supposed to be a Happy Time, no, I'm afraid I
can't do that. Sorry.
However, I see where you took one of my comments personally and I apologize for
inadvertently disparaging your time intensive and carefully controlled plant
growth studies.
Let me rephrase that particular part ...
Pushak quoted as Dave as saying:
>>> "On the other side of the coin, there have been a plethora of
>>> studies which indicate clearly that rooted aquatic plants will not grow
>>> optimally on a sand or other infertile substrate no matter how richly
>>> you fertilize the water column (perhaps the earliest is by Pond, 1905)"
I said:
>>This doesn't jive with my experiences with massive plant growth using plain
>>gravel substrates, undergravel filters and Dupla fertilizers. Just what is the
>>scientific definition of "optimal"? I hope it's more complicated than growth
>>rates. Perhaps the researchers performing the plethora of studies just didn't
>>know how to grow plants!
OK, my interpretation was that Pushak included your quote to prove that you need
a "fertile" substrate to have plants grow well. I question this, in the context
of the aquatic gardening hobby, based on my experience with what Pushak would
call an "infertile substrate" with a well fertilized water column. I have not
run exhaustive studies as you have to define "optimal" growth of the decorative
plant species I maintained in the tank, but they were growing fast enough that
we had to prune their mass by 1/2 every two weeks. For me, that was "optimal
enough", non-scientifically speaking.
My pointed remark about researchers not knowing how to grow plants was directed
more to authors who write general hobbyist type books (like Rataj) than to real
scientists doing real science.
>From your comments, I suspect that you mean "infertile" in a more exact sense
than Pushak uses, i.e., plain sand with nothing else - no fish waste, no water
circulation to pull nutrients down to the roots, etc. Is this correct? I
certainly have no argument that a substrate with no nutrients would not produce
desired growth compared to a substrate with even a modicum of typical aquarium
waste and detritus. It is obvious to me and I hope obvious to most readers that
many plant species we maintain require nutrients in the root zone. Pushak and I
seem to disagree on how much and how to get it there.
If I am still off-base, perhaps we should try to define more carefully the
varying types of substrates we use, going from an impratical to achieve
"sterile" substrate to the full on organic cesspool. There is clearly a range of
substrates that work very well in an aquatic gardening environment and we need
to be able to accurately describe the various types without resorting to
pointless and unverifiable "this works better than that" claims.
Happy Holidays,
George
by George Booth <booth/hpmtlgb1.lvld.hp.com>
Date: Tue, 30 Dec 1997
> Date: Mon, 29 Dec 1997 21:04:03 -0800
> From: Stephen Pushak <teban-at-powersonic.bc.ca>
>
> > What is the proper level of CEC in the substrate?
>
> There is no such thing as a proper level of CEC.
But more [than laterite] is better, according to your theory? If I may
summarize your original first paragraph:
"... laterite has a relatively low CEC ... Improving the CEC of your substrate
is quite easy ... [improvement methods listed]"
If there is no such thing as a proper level of CEC, why are you trying so hard
to convince the readers of APD that laterite does not have enough?
> It is well understood
> that soils with a higher CEC value are better able to retain nutrients.
I've never argued with this fact since that's pretty much the definition of CEC.
What you keep implying is that a substrate needs a higher CEC than laterite
provides to retain enough nutrients for good plant growth. This, to my
knowledge, has not been proven anywhere. Quite the contrary, good plant growth
with a laterite based substrate has been demonstrated at the hobbyist level by
many people, including myself. Let the readers judge for themselves; my website
is [location
updated by editor]. Dueling web sites at 20 paces. <g>
> There is a table of CEC values for various substances in my
> substrate article. Please note that laterite also has a CEC value.
I wish you would note that also. Which gets us back to the original question:
why do you think this number is too low for aquatic gardening purposes?
> One
> of the major points of my post was that laterite and kitty litter are
> quite different in their characteristics.
Your first couple of sentences mentioned that. The major point of your post
seemed to be that phosphate may be lacking in the substrate (or your substrate,
at least), leading to the need for Jobe's plant sticks. Yet, a laterite based
substrate helps sequester phosphate right where it's needed. Go figure.
> I have never heard of specific plants requiring a specific CEC value.
> I'm not familiar with the laboratory techniques for measuring CEC and I
> don't think we should mislead people into thinking there is any value in
> attempting to measure it.
Yet you suggest that more CEC is better and give us many techniques for adding
CEC. Maybe I'm alone in my belief, but I think one should have some measure of
how much CEC is already there and how much CEC is actually needed before one
starts adding extra CEC to an aquarium. Luckily, I believe that Dupla knows how
much CEC is needed and I follow their instructions for adding it with the proper
amount of Duplarit-G.
> I don't believe that the CEC of laterite is it's key advantage. You are
> pretty quick to criticize empirical results as non-scientific but we
> should remember that the only evidence we have about laterite is
> empirical. We can only surmise that laterite and other substances help
> to bind phosphates in the substrate.
I am pretty quick to criticize empirical data masquarading as scientific data.
If I have ever couched any claims about laterite as other than empirical, I
would appreciate knowing about it. I am not a scientist but my wife is, so I
know what science is about and I am pretty careful how I phrase things in this
forum so as to not imply any scientific results.
> Yes, experiments by Barko and Smart clearly indicate that sediments with
> higher than 5% organic content actually inhibit growth. Sediments with
> lower than 5% organic content grew plants better as the organic content
> increased.
You are implying that organic content is good if kept below 5%. How do mere
hobbyists determine organic content already in the substrate and how much of
what is needed to get to 5%?
> > Is this by weight or volume?
>
> By weight.
>
> > I have 200 pounds of gravel. Does this mean I need 2 to 10
> > pounds of humic material?
>
> No. Your layer of gravel is probably too deep for that. I would suggest
> that it would be more appropriate to use a layered approach similar to
> what is advocated for laterite.
I don't believe you've mentioned depth before. Mine is 3.5" deep. What's the
deepness limit for using humic material?
> > This doesn't jive with my experiences with massive plant growth using plain
> > gravel substrates, undergravel filters and Dupla fertilizers.
>
> You are assuming that your Dupla substrates are infertile. If your
> substrate helps to grow better aquatic plants, it can only be because it
> is fertile. Any other theories?
"Infertile" is your definition, not mine. Maybe we need some new definitions or
terms that aren't quite so loaded with implication. How about:
Dupla-style: "just right"
Fertile: "loaded time bomb"
> I will qualify really high lighting to mean 4+ wpg or partial sunlight
> and significant chelated iron to be greater than 0.2 ppm.
Yeah, I would qualify those as pretty extreme since the general recommendation
is 2-3 wpg and 0.15 ppm.
> If your aquarium is in the range of 1-2
> wpg, then you probably won't need the high quality iron test kit that
> George needs. ;-)
Guess I better trade mine in for a low quality kit since I have 1.6 wpg. :-}
And what on earth does iron test kit quality have to with anything?
> > Let us know when you find a substrate recipe that works for more
> > than a few months.
>
> I have George. Since when did we make a rule that says you're not
> allowed to periodically fertilize the substrate?
If your recipe was the 96 step process you posted a while ago, I guess I'll just
stick with my infertile, unoptimal methods.
Cheers,
George
by George Booth <booth/hpmtlgb1.lvld.hp.com>
Date: Wed, 31 Dec 1997
> From: Stephen Pushak <teban-at-powersonic.bc.ca>
>
> George is not a spokesman for my views ... My opinion is
> that he is taking perceived criticism of laterite far too personally.
> From: "Dennis J. Harney" <harneyd1-at-muohio.edu>
>
> I believe you fellas are speaking of two different things here: optimal
> growth and fertility ... Definitely an
> interesting discussion (probably for another forum).
> From: Pete and Kellie Schmidt <petes-at-nas.com>
> Subject: Dupla spokesperson / Kitty litter / Laterite / Soils etc
>
> Come on George, you are making this not so much fun.
I apologize if I made this discussion too interesting. Jim Kelly posted an
excellent "low cost substrate" article many years ago which was the first time I
had seen a table of CECs for various materials. Laterite was last on the list
with a value of "4" and the implciation, if my memory serves, was that one would
want a higher value in the substrate. Jim suggested adding vermiculite (CEC=150)
at that time.
I challenged the assertion that the CEC of laterite was too low then and I still
do when it comes up. I guess I should stop beating a dead horse. No one seems
to know the answer and fewer yet seem to care.
OK, just one more whack. Perhaps someone who feels like doing a wee bit of
research could consider if the CEC value stated for "laterite" (4) is a true
value, representative of all laterites, or if it was an average, much like the
average content of iron in soil has a value but was shown to be a relatively
useless measure since the range of iron content in soil was quite large.
Cheers until Jan. 5,
George
by krandall/world.std.com
Date: Sat, 03 Jan 1998
Steven wrote:
>CEC thing may be only a single facet of the whole thing. How about
>toxicity from metals? how about humic acids from peat? I think that's
>why Dupla went with laterite. Maybe that wanted to use clay initially
>but had toxicity problems. Lateritic clay would be the next best thing
>without introducing organic systems to the equation. If you start mixing
>humus, peat, soil etc with laterite, why bother with the laterite?
I agree with that. Same goes for those who choose to use kitty litter.
_Why_ do people spend the money for laterite, then go and add an unknown
like kitty litter? It's not needed. OTOH, if your goal is to do things on
the cheap, use the kitty litter if you choose, and you can add a cheap iron
source like micronized iron. I think that too much is made of the expense
of laterite in any case. considering the cost of setting up an aquarium
even the most expensive laterite is a mere drop in the bucket.
>Laterite works only because it is part of the whole Dupla system.
This is not so. Many people including myself have successful, beautiful
planted tanks using laterite with no other Dupla products, and without
using heating cables or other substrate heating.
I have worked some with soil substrates, and I can still not, in all
conscience, recommend any substrate other than a gravel/laterite substrate
to the many novices I work with, at least for their first tank.
>If
>your goal is to avoid the commercial approach using materials at hand
Let's be clear that for most people, the components for PMDD's are not
"materials at hand" for many people. I've seen a lot more posts from
people searching for various PMDD ingredients than I've seen people having
trouble finding Dupla products. If you want to claim that your methods are
cheaper, or that you gain satisfaction from the DIY approach, fine, but it
sure isn't easier or more readily available.
>and a minimum of test kits, the approach will be different. It's an
>apples and oranges thing.
Sorry, but I use laterite in most tanks, and my test kits become outdated
far before I use them up. I've never been a proponent of the test tube
school of aquarium management.<g>
Karen Randall
Aquatic Gardeners Association
The Krib
Plants
Plants