Chemi-Mat is a revolutionary 12" x 12" phosphate filter pad for salt and freshwater aquariums. Simple and easy to use - just drop it into your aquarium, and it starts removing phosphate within 24 hours. After a total of 36-48 hours, simply remove the pad and throw it away. There`s no physical breakdown of the pad and no phosphate is released back into the aquarium. Chemi-Mat contains no chemicals, does not affect pH, and eliminates almost all PO4.