My Fish Tank by Lam Nguyen

Carbon Dioxite

What I currently have:

Tank:	5lb pressurized CO2 gas.
Reactor:	Powered DIY reactor.
Controller:	Solenoid valve with on/off timer set to turn on 1 hour after light is on and 1 hour after light is off.
Bubble rate:	About 3 bubbles a second when on.

Why do we need CO2 ? I read on the Internet that with CO2 injection and with high light the plant will really grow well. Recently (July 2002) I read a small article on Star Tribune news paper that wrote that plant take 6 CO2 molecules, 1 H2O molecule and use light energy to create 1 molecule of sugar and 6 molecules of oxygen. The sugar is then use as energy source for plant to grow. This process is called photosynthesis. In a heavily planted fish tank when all the plant photosynthesis, the oxygen they generate can saturate the water. When oxygen level in the water is saturated, oxygen in the plant start to push out of the plant and form a tiny stream of bubles. Some of the streams of bubble are so tiny, it rises up to the surface so ever slow, it moves back and forth with the water current, it very beautiful to look at (Well, I think so).                    When I decided to add CO2, I tried the yeast method. The CO2 reactor was an inverted bell that was a bird water bottle. I brought it at Pet Co. I discarded the bottom tray and use the top acrylic as an inverted bell. Then I carefully drill a 1/2 inch O.D. hole on top of the bell and welded (acrylic term for gluing them together with solvent) a 2.5 inches by 1/2 inch O.D. clear acrylic tube. This inverted bell with a rigid tube on top is then connected to the filter return output via a 2 inches plastic hose acting as a coupling so the reactor can quickly remove, clean, and put back into service. The reactor is put inside the tank at one of the corner. CO2 is then injected inside and under the bell. CO2 bubble rise up, meet the water return stream, tumbling around and dissolved complete into water column. This design is neat in a way that I don't need a separate bubble counter or ceramic disc in glass reactor that cost $40 bucks. It's 2 in 1 kind of reactor.

For 2 months I tried the yeast method with a 2 litters pop bottle. I have a difficult time convince myself that the cap with a 1/8 inch tube is sealed. The yeast method seems un-reliable. The pressure and the CO2 it generated seem never enought for my fish tank. So I start to search around the Twin City and comparing prices for a pressurized CO2 tank. Finally, I found my CO2 tank at a company called Toll Gas Welding and Supply store located in Brooklyn Park. The 5lb filled tank cost $67.63 and a"CO2" dual gages for $47.93. So as of June 2001 I have a pressurized CO2 injection system. Purchasing a pressurized CO2 was part of my master attack plan against the algae. By providing the plant with all their needs, I am hoping for the plant will out-compete the algae. Well, after more than a year of running the pressurized CO2, I can say that the CO2 stratergy definitely works. The algae strength's seem reduced significantly. I emphasized the word "strength". The plant are growing well too. And when their photosynthesis is in full production capacity, the tank looks wonderful. The whole tank bubbles like champagne, big bubbles, small bubbles, streams of different sizes of bubbles. And this happened everyday. It is beautiful to look at.                    But, I have to improve the CO2 delivery system (of course, one must always improve one's ugly design). The inverted bell is nice, great and works, but it must located inside the fish tank. I do not like anything inside the tank other than fish, plant and maybe water. So I relocated the reactor to my external ex-bio filter. But because of the ex-bio filter design, I have to change the reactor design.

But of course, it still can be improved upon again on the next fish tank. The new design is to include a bubble redirector. The current CO2 reactor tends to leak some CO2 bubbles because of the straight down flow water direction of the reactor chamber. The bubble did leak some but not much, but it still is annoying me.

A future CO2 reactor design would be a square acrylic box with a bubble redirector to redirect the bubble back up so that they continue remains in the water stream, tumbling and dissolved. Also, the external bio filter renamed as external service tank, would be deeper. The CO2 reactor would locate as near the bottom of the external service tank as possible. This arrangement will help the CO2 dissolve faster as the bubble being injected at the bottom of the tank will under more pressure from water than the top of the tank.

With this CO2 reactor design I don't have to worry about CO2 dumping. Actually, I never have it happened to me before. I changed the CO2 tank when the pressure dropped to 400 PSI. If the CO2 dumping did occured, the CO2 reactor chamber will over fill quickly and spill excess gas before it has a chance to dissolve. The only way for the CO2 dump to have any chance of doing any real damage is cause by the needle meter valve. If the needle valve slow down the rate of the CO2 gas then that would be a problem. This CO2 reactor designed to dissolve CO2 gas into water fairly quickly. It is able to dissolve CO2 gas with a bubble rate of 40 bubbles a second. This is an eye ball estimation only. I could not count the bubble that fast nor does the bubble actually form at about 1/8 inch diameter at that rate. The rate I feed it into the reactor was about four 3/4 inch diameter bubbles per second. At this rate of incoming gas, the CO2 gas pocket in the reactor chamber remain constant. The pH would drop very rapidly to 6.0. But remember that my CO2 reactor located in an external service tank. The external service tank contains about 2.5 gallons. So even when the pH in the service tank drop to 6.0, it would be some time before the pH in the main tank begin to drop.                    I set my regulator at 2 PSI. So if the CO2 dump occurs, the initial pressure would be about 350 to 400 PSI. At that pressure the feed rate would be very much faster that normal and spillage would happen. The damage would have to be near the end of the dump where the pressure drops to near 30 to 40 PSI. At that pressure, I believe the dissolve rate of the reactor would consume more CO2 gas than the needle valve allowed.             There are 2 ways to help minimize the the CO2 dump. One is to add a second lo pressure regulator that have a range of 0 to 450 PSI. Set the first regulator to 20 PSI and second regulator to 1 or 1.5 PSI. The idea behind this dual regulator is that when the dump begins, the the second regulator would catch the pressure and continue to regulate the CO2 gas. However, if the second regulator fail to regulate the CO2 gas, then the needle valve is our final barrier. Since the needle valve normal pressure was 1.5 PSI, you would have to open the needle valve up a little bit more than say at 5 PSI to have the same bubble rate at 5 PSI than when it set at 1.5 PSI. This setup will allow more CO2 gas to flow during the dump situation. And this is what we want to happen during the dump. When the CO2 gas flow much faster into the reactor chamber than the reactor's dissolve rate, it will cause an overflow and spill excess CO2 gas.             The second way to minimize CO2 dumping is to shorten the reactor chamber to reduce time to spillage. This can be done by drilling a couple of hole say 1/4 inch at predetermine length of the CO2 reactor chamber. Drills hole rather than shorten the reactor chamber will help keep the water flow parttern inside the reactor remain the same.             Of course, one could always keep an eye on the gauge and change the tank when the pressure drops below 500 PSI. And, of course, one could always keep on monkeying with one's design until it work perfect the way one want it to. (Too many ones, I think)

A few pictures:

Current CO2 reactor inside service tank

Detail design of future CO2 reactor

Yeast inverted bell CO2 reactor picture

Picture 1 Picture 2

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