Healthy Ponds 10191 2,500 Gallon Refill 4 pack  (Older Model) Natural bacteria and enzyme blend reduces excess nutrients, sludge and ammonia, resulting in improved water quality and clarity Treats up to 2,500 gallons Each refill provides 24/7 water conditioning for 30 days Saves time and effort, with no mixing, measuring or mess Safe for humans, pets, fish, birds and plants