Phosphorus (phosphate), an important plant nutrient, is lacking in natural waters (0.001 - 0.01 mg/l). During their long evolution, plants have adapted to this lack and therefore require very little phosphorus for growth. High concentrations of phosphorus compounds, in the aquarium often more than 100 to 1000 times the natural level, leads to an explosive increase in unwelcome algae. Regular checks of the phosphate level in the water using a phosphate test and the prompt application of JBL PhosEx ultra prevents this risk. Levels up to 0.5 mg/l may be tolerated in a freshwater aquarium, and, in a saltwater aquarium, levels below 0.1 mg/l are desirable.JBL PhosEx ultra removes phosphate from fresh and sea water. Easy to use with the practical net bag. In a normally stocked 200 l fresh water aquarium or 100 l marine water aquarium contents are sufficient for 5 - 6 months (package contents absorb 18,000 mg of phosphate) the bag is put easily between the filter media in the aquarium filter.