Convenient use drop-in blocks control algae in ornamental fish ponds Extremely easy way to keep nuisance algae growth under control Clear cloudy water and remove algae from water features and fountains Keep algae under control and pond water clear for just pennies a day! TetraPond Pond Block makes effective algae control as simple as tossing in a tablet/block once a month. Clears cloudy water and controls algae in ornamental fish ponds, water features and water fountains. Convenient algaecide block takes the guesswork out of measuring doses. TetraPond Pond Block is not recommended for ponds or water gardens with live plants. One block treats up to 250 gallons for 30 days. Use only as directed. 4 blocks included.