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Aquariums And Types of CO2 Systems


In planted freshwater aquariums, one must use multiple techniques to promote healthy and thriving plant growth. This includes proper substrate, adding CO2, lighting, and fertilizers. I will now explain the use of CO2 systems and how they work and benefit your aquarium.

First off, for those of you who do not understand the basics, plants need energy, as do we as humans. They get this from water, sunlight, nutrients in the ground (or water in the case of aquariums), and CO2. In aquariums, adding CO2 to the water helps promote healthy growth of the plants, and differences can easily be seen. Plant in general will grow larger, and taller with the added CO2. And yes it is true that fish take in Oxygen and give of CO2 as a waste, but this is not enough for you tank. Adding a CO2 system to your set up will be beneficial. A planted tank will show significant differences when a CO2 system is added.

Yeast CO2 reactor system:

This is a very common inexpensive CO2 system. Basically, yeast, a type of fungus used in baking, consumes sugar and releases CO2 gas as a waste. We as aquarists use this to our advantage. Through my journey into the exotic pet world, yeast has proved itself useful as many things, including producing CO2.

To capture the CO2 from the yeast, one must use a sealed container where the yeast does its work. The way these systems work is pretty simple, and maintenance is simple and easy as well. Firstly you add water, I find that using tap water works fine, but if you get town or city water, there may be added chemicals that may cause problems for the yeast, so maybe use drinking bottled water. Most systems that you purchase will let you know how much to fill it up, I fill mine up almost to the top, and then I add yeast, and sugar. I add about a half a teaspoon of active yeast and a teaspoon of sugar. Many brands also sell a stabilizer which is supposed to aid in the production of the CO2 and I feel it makes it last longer before I must change it, but I often do not use it. I change the yeast, rinse out container every month or so.

The container is attached to airline tubing, leading from the container top that often easily unscrews, down to the diffuser. There are two types of diffusers, one where the bubble of CO2 travels up a spiral or gradual ramp type diffuser to increase the time that the bubble is in contact with the water, and the other one user is often glass. The glass ones are harder to find, but the way these work is that they decrease the size of the bubble, increasing surface area that touches the water.

CO2 bells are also used, more uncommon, these trap CO2 bubbles under them and the CO2 is slowly released into the water. Basically the bell is an upside down bowl placed over the airline tubing the CO2 comes out of.

The yeast itself is living, so it must be kept in ideal conditions. I keep my reactor at room temp, and keep the yeast itself in the refrigerator until ready to use.

You can purchase these simple set ups from local fish stores for anywhere form $20-$40. Or make your own. Later in this article you will read how to make you own system.

Pressurized CO2 system:

Pressurized CO2 systems are great for larger tanks. The yeast reactor systems should be used for up to about 29 gallons in my opinion and experience, and then pressurized should be used for larger tanks. They last longer and work more efficiently; this expensive solution is actually fairly simple. Expensive to set up ($100 ) it is not too costly to maintain. I find that getting it filled at machine shops and paintball places works well. Most though are the larger canisters that must be filled at welding places. These must only be filled every month or two and you have control over the CO2 flow. The way these work is a canister, pressurized with CO2, then it goes through a pressure regulator, then through the airline tubing into the tank, and then the bubbles are then diffused into the water with the option of methods described above. And another common way of diffusing the CO2 is a reaction chamber. These work by the water flowing through it and the bubbles of CO2 staying in the chamber and diffusing into the water that way. These tend to be a bit more costly ($30-$40) but very efficient and worth the cost. In general I would highly recommend the pressurized systems over anything else, but cost can be a factor. And remember, that these can still work great on small nano tanks, 5.5g, 10g and so on. If you do end up placing one on a smaller tank, try using a paintball canister. Cheaper and smaller, they will work great on the nanos.

Do it yourself CO2 reactor and diffuser:

Here I will describe how to make your own CO2 yeast reactor, aka DIY CO2 reactor. It is cheap, works adequately, and is easy to make. Also included is a simple home made recipe for the canister.

DIY CO2 yeast reactor: Materials needed…

Procedure: Take the cap (should screw on) and use a drill or nail and make a hole, smaller than the airline tubing into the top. Use pliers and pull the tubing through it, and it will make a seal, no glue needed. Take the tubing and attach it to the diffuser in the tank.

DIY Diffuser: Couple options, buy one, or make one.

Buying one:

Making one: Materials needed…

Procedure: Drill or poke another hole in the siphons side, place foam in the bottom to block the opening, and then place the pump on top. Turn the pump on and the water will be pushed into it, while bubbles are rising up into it towards the pump. This will aid in the diffusion of the CO2.

People often also just stick their airline tubing directly into the filter and the movement of water will help the CO2 diffuse, not super efficient, but works fine and not hassle.

Recipe: The basic simple recipe is as follows.

I have no idea what the baking soda does, I guess it acts as a regulator, but I have found it works fine with and without it with little difference.

CO2 Tips:

When using CO2 systems, a glass cover works fine, no need for egg crate or no top. But you can have no top. The CO2 must stay in the water to be used, so trying to increase diffusion with the water surface (increasing ripples, power heads agitating water surface) is not needed and can decrease the CO2 in the water, defeating the purpose of having your expensive system. Just remember, do not overstock a planted tank, and you should be fine. When making a planted tank, focus on the plants as much as the fish.

Negatives to the CO2 system:

CO2 systems are good for planted tanks, but if you are looking for heavily stocking your tank (a sometimes frowned upon idea) CO2 systems would not be good to do. With planted tanks, adding the extra CO2 can be good for the plants, but when too many fish are added, you are basically suffocating the fish. So in general if you wish for more fish, do not have real plants. If you still want plants, look into fake plant, they can still give a nice look. And other than that, make sure that you have nice aeration in the tank, either an air stone or a good water flow at the top of the water, creating enough ripples in the top. Another negative to the CO2 systems may be cost for the higher end set ups, but other than that, they can be very beneficial to your planted tanks.


DIY CO2 systems are obviously the cheapest, but least efficient. For any planted tank that you plan to put time and money into, invest in a pressurized CO2 system. This will greatly improve the overall look of the planted tank. But do remember that pumping CO2 into the water will limit number of fish in the tank. This article is to be used as one source for your research. Please do continue research and get other peoples’ opinions before doing anything. Most of this has been put together from my own experience and research on aquariums in general.

Article is written by Mike Gioia exclusively for; 3/10/08.

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