When injecting CO2 into a planted aquarium, it is important to know how much CO2 is actually getting dissolved. Otherwise, this is like driving without knowing your speed; one day, you’ll hit the ditch. But what is the right amount of CO2 and what are the consequences when CO2 is too high or too low? To help figure this out, I have put together some information found over the years. If anyone wants to add to this, please use the comment box bellow.

Too much CO2
First, your are wasting CO2 and money. In addition, excess CO2 can lower the pH level dramatically and severely stress your fish. In extreme situations, your fish will die of anoxia.

Not enough CO2
This one can be a little confusing. While 5ppm of CO2 can be enough in some tanks, 20ppm can be too low in some other tanks. Basically, your light is what makes the difference.
As little as 10ppm of CO2 could be enough for some tanks but, if you add more light, CO2 would start becoming a more limiting factor for your plants which allow algae to grow better (algae need less). There is a competition between plants and algae so if you limit plant grow, you help algae growth better.

Unstable CO2
Both plants and algae adapt to CO2 in their environment. To do this, they produces what’s call the Rubisco. The Rubisco is an enzyme that is used for carbon fixation. In a low CO2 environment, plants and algae will produces more Rubisco so they can fix carbon from the KH (-HCO3). When there is plenty of CO2, plants and algae no longer need the Rubisco so they simply get rid of it.
Problems show up when CO2 is unstable because algae are much faster to adapt to low CO2 than plants. So everytime your CO2 is changing, algae have a chance to outcompete the plants.

The Right CO2 level
All tanks are different, so it’s difficult to tell how much is enough. As a rule of thumb, tanks with less than 2 watts per gallon usually don’t need additional CO2. You fish will take care of that.
With more light, fish alone won’t produce enough so this is where CO2 injection comes into play. Most aquarist have to say that 20-30ppm is the optimum CO2 level for tanks with more than 2 watts per gallon.

Whatever how much CO2 is injected, I think the most important thing is to know how much is actually getting dissolved into the water. Knowing this will tell you a lot. You must work with known variables in order to know why things are doing well or wrong and make adjustments when needed. For more information about how to monitor CO2 levels, read how to measure co2 in a planted tank

Article written by Patrice Lapointe for AquariumsLife.com

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