"The 7-Day Pyramid Fish Feeder for Fresh and Saltwater Fish by API is the ideal way to feed your fish whilst you are away. With a soluble outer shell which gradually dissolves releasing food into your aquarium, makes the 7-Day Pyramid Fish span "Feeder the great way to cover holidays or any seven day period away. Each pack comes with one feeding block containing a complete diet fish food, which is suitable for tropical, coldwater and marine fish. On the fourth day, the 7-Day Pyramid Fish Feeder will release a cube of tubifex worms as an extra treat for your fish. Each feeding block contains enough food to feed up to 20 average sized fish for 7-10 days. The 7-Day Pyramid Fish Feeder is NOT SUITABLE for fish bowls or aquariums without adequate filtration; water circulation is required for the block to properly dissolve