The Dymax co2 indicator solution 10ml is a liquid reagent that is used to measure the co2 levels in a planted aquarium. It is designed to work with the Dymax crystal co2 indicator, a glass device that changes colour according to the co2 concentration in the water. The solution is easy to use and comes in a 10ml bottle. To use it, you need to fill the indicator with 5 drops of the solution and place it inside the aquarium. The solution will react with the co2 in the water and change colour within 1-2 hours. The colour will indicate whether the co2 level is low (blue), optimal (green), or high (yellow).