Healthy Ponds 10515 Stock Tank Water Cleaner Value Pack with (3) Dispensers & (18) Refills Natural bacteria and enzyme blend reduces excess nutrients and sludge, resulting in improved water quality and clarity Treats stock tanks up to 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, livestock, pets and birds