TetraPond Pond Block helps to clear cloudy water and control algae growth in ornamental fish ponds These blocks are ideal for containerized ponds and fountains not recommended for use with live plants Use one TetraPond Pond Block for water volumes between 100 gallons (380 L) and 250 gallons (950 L) For the initial dose add one block for each 100 gallons (380 L) of pondfountain water For regular maintenance replace block(s) after previous block(s) have fully dissolved usually after 30 days Algae are primitive plants that via photosynthesis combine water and carbon dioxide to form sugars for energy and growth Algae can obscure colorful fish and deplete valuable oxygen No pond is ever totally free of algae but in a balanced environment and with the right treatment methods algae can be kept in check Since 1951 Tetra has developed the worldAs most comprehensive body of fish food knowledge and fishkeeping enthusiasts have looked to the brand for products and solutions that add ease and beauty to their home Whether youre an experienced hobbyist or just starting out Tetra has everything you need from a large variety of quality fish food and innovative equipment to test kits and decor