Pura (Magnavore) APU00401 Phoslock Aquarium Filter Media for 900-Gallon Tank, 454gm Phoslock is the benchmark ferric hydroxide media for total phosphate removal in all aquaria Permanently and irreversibly binds phosphate and silicates Feature removes large quantities of phosphate, arsenic, silicates and other heavy metals and thus greatly reduces propagation of algae Phoslock can be placed inside of sumps, refugiums, canister, power, pond and corner filters next to uplift tube on UG filter plate This 454-gram Phoslock comes with 6-inch by 12-inch 300-micron media bag; treats 900-gallon aquarium