Simply place the block into the aquarium and leave it. The block will then slowly release small particles of food when disturbed by the fish looking for food. If any of the food block is uneaten on your return, carefully remove the remains and discard. Each block contains sufficient food to care for 12 small tropical fish or 5 medium size goldfish for up to 4 days. For less fish carefully cut the block into an appropriate size. Discard any powder produced after cutting.