Salifert's Potassium Test Kit provides a quick, accurate, and reliable method for measuring potassium levels in your reef aquarium. Potassium test kits are notoriously difficult to use on average, but Salifert's kit provides a method to take potassium readings without the stress and headache, giving you a precise analysis in minutes. In naturally occurring saltwater, potassium levels usually equal around 400 ppm. Coral start to become potassium deficient, potentially losing coloration, around 350 ppm and lower. Potassium test kits let you know when it's time to replenish potassium levels before color loss occurs in your beautiful coral. This kit provides approximately 40 tests per box.