The solution in the drop checker changes color to indicate the level of CO2 in your aquarium water; blue indicates a lack of CO2, yellow indicates too much CO2, and green indicates the desired level of CO2. Depending on the color of the drop checker you can adjust your CO2 dose until the desired level of CO2 is reached.
The drop checker should be used in conjunction with a bubble counter so that fine adjustments to CO2 dosing can be achieved. Always make small changes to CO2 dosing, particularly if increasing the dose.
The kit includes a pre-mixed drop checker solution, which is added directly to the drop checker. The solution comes in a 15ml dropper bottle for ease of use. The solution will last 6 months if changed on a monthly basis.