Aquarium CO2 Drop Checker Solution 15ml. 

It consists of a pre-made 4dKH solution containing the appropriate amount of indicator. Easy to use, no mixing required. Simply open cap and fill CO2 checker.

1. Fill the drop checker 2/3 full of CO2 Drop Checker Solution
2. Install drop checker inside aquarium
3. Optimum CO2 level is reached when indicator solution is deep green
4. Replace CO2 Drop Checker Solution minimum once a month to maintain accuracy

When the drop checker is submerged in the aquarium, the carbon dioxide will outgas from the aquarium water into the airspace of the drop checker and will eventually be absorbed into the indicator solution. The carbon dioxide gas will seek a point of equilibrium between the indicator solution and the aquarium water. As equilibrium is achieved, the color of the indicator solution inside of the drop checker will change based on the concentration of CO2 in the aquarium water.