Aquarium Pharmaceuticals Phos-Zorb for API nexx & Rena SmartFilter selectively removes ammonia, nitrite & nitrate from freshwater and saltwater aquariums. Removes phosphate, a by-product of fish metabolism and decaying organic matter and an additive in some tap water supplies, aquarium products and filtration media
Size 4 - Fits API Nexx Filter & Rena SmartFilter
Size 6 - Can be used on any aquarium filter - treats up to 55 gallons
INSTRUCTIONS: Easy-to-use pouch works 2 months, change regularly for clean & clear water.