If you want to prevent algae growth in your water reservoir, the Aquapro Pond Algae 20g Block is made for you. The Pond Algae block has been made with the ingredient diuron to work as a preventative of algae growth within your pond or water feature. Each block can treat 800 litres of water, or you can break it into 4 segments to treat 200 litres at a time. Best used in conjunction with a 24/7 pump to allow for water circulation of the diuron to ensure it effectively blocks algae growth. If you have an initial algae problem, it’s recommend to first treat it with the Aquapro Algaway, and then use this pond block to ensure it doesn’t bloom again. The Algae block is harmless to plants and wildlife if dosage is adhered.