Phosphate Sponge 2 gallon bucket, 10 lbs. treats 960 gal., Kent. A granular zeolitic medium which works by two methods. 1) It slowly directly absorbs small amounts of ammonia that re released by fish and natural processes, and 2) it fosters anaerobic bacterial denitrification due to its physical porous structure. This denitrification slowly reduces nitrate levels in the aquarium. Nitrate Sponge prolongs the time allowed between water changes by keeping nitrates low! This item is a special order item only.