Dennerle CO2 Long-Term Test Correct + pH for continuous direct CO2 measurement. Conventional long-term CO2 tests are filled with a mixture of aquarium water and indicator this involves various disadvantages one being that the acids which are present in all aquarium waters (e.g. humic acids nitrate) can distort test results substantially. The Dennerle CO2 Long-Term Test Correct employs a ready-to-use special CO2 indicator which is used on its own rather than in a mixture with aquarium water. The benefits of this system include: SAFETY: The CO2 Long-Term Test Correct measures the CO2 content and indicates the actual CO2 content correctly at all times - irrespective of any other acids in the aquarium. SIMPLICITY: No additional measurement of carbonate hardness is necessary. Only a single colour-matching scale is required. ACCURACY: The CO2 Long-Term Test Correct allows direct determination of the CO2 content in milligrams per litre. The test is equally efficient at low carbonate hardness levels. Complete set comprising of: - Test container. - Special CO2 indicator. - Six-colour matching scale.