AquaMaxx Phosphate Out Pro High Capacity GFO Filter Media - 1 Quart 32 Fluid Ounces or 1 Quart Phosphate Out Pro holds up to twice the amount of phosphate compared to standard GFO. Rinse before use For saltwater aquariums, use 1/2 cup for every 50 gallons of aquarium water Test phosphate levels and replace media when levels begin to rise (approximately every 3-6 months)