How Much Co2?

Introduction: Each and every aquarium has a different balance. Different plant masses, bio loads, filtration, lighting and fertilising regime. In order to achieve a clean and healthy aquarium with Co2 injection, we need to ensure the appropriate amount is used. Otherwise we face algae problems and risk the health of our livestock. Luckily, measuring Co2 is not too difficult and can be done in one of two ways. Either with a drop checker or with a pH and KH test kit.

Drop Checkers: While drop checkers are great little devices to approximate adequate Co2 levels, they are probably not the best way. The way they work is very simple. You add a premixed solution to the glass ‘drop checker’ and place it inside your aquarium. The solution then changes colour depending on the Co2 levels in your water column. Blue meaning not enough Co2, Green meaning enough and yellow meaning too much. As aquascapers, we generally try to have the drop checker green by the time the aquarium light comes on. Throughout the course of the day, the solution should become a lime green, nearly yellow colour. This represents the build-up of Co2 throughout the day and is ideal in most aquariums.



KH, pH Method: Our preferred method for measuring Co2 is using a pH and KH test Kit. API makes excellent test kits for both these measurements that are very easy to use. The ideal levels occur in the green zone in the chart below. Say for example the water you are using for your aquarium has a KH of 4.

Co2, pH, KH relationship

As your lights turn on you want your pH to be at 7.0 which will indicate a Co2 concentration of 12ppm. This will build-up throughout the day and because Co2 causes a drop in pH levels, your pH will drop also. At the end of the day your KH will be the same (unless you have added something to increase KH). If your pH has dropped too much and caused your Co2 concentration to reach the orange zone, then you may want to lower the amount you are injecting.

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