Poly-Bio-Marine, Poly Filter, Fish Aquarium Filter Media Pad, 3-pack, 4&rdquo; x 8&rdquo; FOR FRESH OR SALTWATER - The Poly Filter works in both fresh and saltwater marine environments. The Poly Filter will not break down due to salt and will keep all marine environments clean and balanced. COLOR CHANGING TECHNOLOGY  The filter changes color as it begins to catch pollutants, letting the user know whats in the water and when the filter needs replaced. Changes different colors for different chemicals. KEEP CLEANER WATER - Since the Poly Filter removes both chemical toxins and organic waste, the water stays clear without needing changed as often. Keep your tank cleaner, longer. FITS IN MOST FILTERS  Easily fits into many common aquarium filter styles. It can be used with a conventional power filter, plastic undergravel filters, and canister-type power filters. Increase the cleaning power of the system you already have. UNIQUE CHEMICAL FILTRATION - Made from a patented material that filters excess pollutants while leaving trace elements necessary for the survival of your tank. Poly Filter gently removes excess medication after it takes its effect.