How Much CO2 for Planted Aquarium?

In the previous post, I have review Aquatek Co2 Regulator Mini is great equipment to control flowing CO2 in an aquarium. Now on this page, I will share tips on how much CO2 need for your aquarium plants and how to measure CO2 aquarium. So, please continue to read.

When injecting CO2 into your aquascape aquarium, it is important to know how much CO2 is actually needed for a planted aquarium. But how to measure and what is the right level of CO2 for aquarium? And what would happen if is too high or too low?

To help solve this issue, I’ve done some research and gathered some information to find a conclusion for this matter.

Too much CO2

First, your are wasting CO2 and money. Also, 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 of CO2 level as 10ppm could be enough for some tanks. But, if you add more light CO2 aquarium would be becoming a 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

Neither plants nor algae can adapt to CO2 in their habitat. They produce what’s call the Rubisco to adapt to their environment. The Rubisco is an enzyme that is usually needed for carbon fixation which is a crucial role in the reactions of photosynthesis in plants. In an aquarium with low CO2 level, plants and algae will produce more Rubisco so they can fix carbon in the aquarium. When there is lots of CO2, both plants and algae will no longer need the Rubisco to adapt in the tank.

When algae are much faster to adapt to low-level CO2 than plants, the problem will come; CO2 aquarium is unstable. So every time your CO2 aquarium level is changing, algae have a chance to outcompete the plants.

The Right CO2 in Aquarium

All tanks are different, so it’s difficult to tell how much CO2 in Aquariums is enough. As a rule of thumb, tanks with less than 2 watts per gallon usually don’t need additional CO2. Your fishes will take care of that.

With more light, fish alone won’t produce enough so this is where CO2 injection comes into play. Most aquarists 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 to know why things are doing well or wrong and make adjustments when needed. Then, how to monitor CO2 levels in your aquarium?

How to Measure CO2 Level in a Planted Aquarium

When we add little CO2 to water in the tank, will form carbonic acid with lowers the pH. The more CO2 to be dissolved in the water, the lower the pH level.

Over the years, aquarists have found ways to use this reaction to knowing the amount of CO2 concentration dissolved in the aquarium. But, other suspensions such as pH-UP, pH-Down, Discus Buffers and Phosphate will remove the link that makes the most of the water test kit, and calculation methods are not accurate. Most suspensions can be avoided, but, a certain amount of phosphate should always be in our planted tank.

CO2 Table

To correct pH and KH test kits, you can read off the result on a CO2 table. It is cheapest test kit and easy to do by aquarists but, other suspensions present in the water makes it inaccurate. If you use this method, remember to avoid using suspensions and those phosphates will have an effect on your results.

Drop Checker

Another way to measure CO2 in aquariums is with using a drop checker. This method became popular because it allows you to monitor CO2 24/7 by simply looking at it. Additionally, buffers won’t have an effect on results. In my opinion, CO2 drop checker is probably the most accurate way to measure CO2 in aquarium.

Basically, CO2 drop checker is a reservoir that holds a 4 KH solution and a pH indicator. The reservoir is built inside so that there is an opening that allows gas (CO2) exchange between the solution and the water in the aquarium.

As the CO2 gasses off from the aquarium into the drop checker, the ph lowers and the color changes (because of the pH indicator).

It is now easy to know what the CO2 level in the tank is because:

1. The pH in the drop checker is the same as the pH in the tank.
2. We know the solution in the CO2 drop checker is 4 KH.
3. There is no other buffer to make our reading inaccurate.

A Green color indicates a pH of 6.6 which tells us we have +/- 30ppm of CO2 in our tank water.