Treats 2723 litres (500 Gals) for 4 weeks. Clears green blanket weed and green water. No chemicals 100% natural. It contains a built in sludge buster and is plant friendly. It is a probiotic blend of bacteria that will keep your pond healthy and free from algae. The initial dose will start your population of good bacteria and the repeated dose will top up the population to deal with the continued production of excess nutrients in the pond environment. Repeat dose every two weeks during the summer months for a long lasting healthy pond.