The Krib Plants CO2	[E-mail]

A Simple CO₂ Reactor

(Revision A)

This was fine on my previous tanks. However, my current planted tank is larger than my earlier ones, and uses a prefilter and sump, so a certain degree of churning is apt to take place, liberating precious amounts of CO₂ back into the atmosphere. In having to refill the tank for the third time in 9 months, I decided enough was enough and built myself the cheap gas reactor described here.

The reactor's operation is simple: Water passes through the reactor, trickling over the media (bio-balls, shotgun wadding, or in my case, ordinary aquarium gravel), while CO₂ simultaneously bubbles up from the bottom. This gives the CO₂ in the chamber ample time to dissolve into the water before it leaves. It is assumed that all the CO₂ dissolves, so the CO₂ level in the tank will be dependent on the bubbling rate and how fast it leaves the tank water.

Here's a sketch of the unit I built.

The reactor is constructed from a 10 inch section of 1" PVC pipe. At both ends is a PVC el with one side threaded, and screwed into the thread is a drip irrigation manifold. I glued the els to the length of pipe, but only screwed the manifolds into the els. This way, I can change or clean the media later. I used the drip irrigation manifolds because they were cheap and an easy way to get 1" PVC down to 1/8" airline tubing. A hole has been drilled in the pipe as close to the bottom el as possible for the water to exit back into the tank. Finally, I filled the reactor with large gravel because I didn't have anything else handy at the time. I am getting good enough results that I will not bother to change this.

The reactor sits half-submerged in the sump. I tapped off part of the tank return from my sump using a drip irrigation tap, and ran that to top manifold using standard airline tubing. Through the bottom manifold comes the CO₂, also through normal airline tubing. (Some say this will get brittle and break eventually. Hasn't happened to me in two years yet, but I have some silicone tubing ready if it does.) The water returns to the sump through the hole in the side of the pipe.

Initially, I built the reactor with both CO₂ and water entering the top. However, it was pointed out to me (thanks Booga and Dan!) that injecting the CO₂ from the bottom is a better approach because it has more of a chance of dissolving. When I switched to this method, and had the water exit through the bottom manifold as well, I found that the exit water pushed the CO₂ right back out, undissolved. Hence the need for the small hole drilled in the side of the PVC pipe. :) It does what it should now.

I erred on the side of caution when calibrating. Before hooking everything up, I stuck the CO₂ tube directly in the sump to observe the bubble rate was 1 per 3 seconds or so. Then I hooked it all up and adjusted the level slowly over one-day increments to get the level right.

So does it work? I would estimate I went from a bubbling rate of 5/second with the powerhead injection method, to somewhere around 1 per second using the reactor. I'd call it a success!

Cost: two manifolds ($6), misc PVC ($2), teflon tape (had it already), drip tap (had it), rocks (had em) = under $10. If I were really ritzy, I would have built the main tube out of clear PVC or acrylic, but who cares!

	Up to CO2 Plants The Krib	This page was last updated 29 October 1998