The Dennerle CO2 Long-Term Test Correct + pH enables the continuous, direct measuring of the CO2 contenct of the aquarium water. Conventional long-term CO2 tests are filled with a mixture of aquarium water and drop indicator. In contrast, the Dennerle CO2 long-term test Correct + pH employs a high-purity, ready-to-use ampoule indicator which has been developed especially by Dennerle.