Fluval Carbon Filter Media Insert is capable of adsorbing most liquified impurities and dyes present in aquarium water. It does not contain phosphates and will not change the pH of the aquarium water. Fluval carbon is very pure activated carbon that is ideal in both fresh and salt water. The inner matrix structure provides a large porous area that permanently traps organic waste while removing liquid wastes such as urine, dyes or many other impurities from the water. The result is sparkling clear aquarium water.