Tetra Laborett contains all of the test kits you need for checking the water quality in planted and community aquaria, and also for checking the general condition of the water for fish. pH is a measure of how acidic the water is, KH (carbonate hardness) reflects the ability of the water to maintain a stable pH, GH (general hardness) reflects the total mineral content of the water, nitrite is toxic to fish and indicates how well the filter is working, and carbon dioxide levels are important for healthy plant growth. This Kit Tests for: Nitrite pH KH GH CO2