The JBL ProAqua Test K Potassium is designed for measuring and doing routine checks of potassium content in freshwater and marine water aquariums within a range of 2 - 15 mg/l (ppm). Salt water has a potassium concentration of around 390 - 400 mg/l, which, however, is only consumed in small amounts. Excessively high potassium concentrations can endanger sensitive animals such as shrimp.Potassium is one of the macroelements which is absorbed very quickly and effectively within a few hours and stored temporarily by plants in fresh water. Growing plants require more potassium compared to other elements. As a result, potassium concentrations can drop to a minimum range, causing plant growth to stagnate, even if the aquarium water is fertilised regularly (e.g. weekly). Potassium levels in mains water are usually too low compared to natural biotopes, particularly with regard to calcium and magnesium concentrations. We recommend daily measurement of the potassium concentrations of your tank w