Kent Marine Phosphate Sponge, 4-Quart (Two Jars - 2 Quarts Each) Kent Marine Phosphate Sponge, 4-Quart Total (Two Jars - 2 Quarts Each) Phosphate sponge is a ceramic medium which will adsorb phosphates quickly when placed directly in the water flow Works in fresh and saltwater aquariums or ponds Bring about 1-ppm of phosphate or silicates down to less than 0.05-ppm in a 120-gallon tank for every dry quart of medium Also absorb moisture for use as an air dryer for ozone and can be renewed over and over in moisture removal service