The Elos HR Phosphate Test measures values from 0.008 – 0.14ppm. Phosphate build up in the tank appears to be a fairly common problem in marine aquariums. In Natural Seawater the Phosphate level is normally about 0,06 mg/l, and can reach 0.01 ppm in reef areas. Elos AquaTest Phosphate HR, is intended to be used in aquariums, and measure Phosphate level in a range between 0.008 and 0.14 mg/lt. of PO4. Good for at least 100 tests provided it is used and stored correctly.