Small starfish-shaped blocks made from a calcium matrix that slowly dissolve to release fish food into the water. King British Weekend Feeders are suitable for all coldwater & tropical fish. They are small starfish-shaped blocks made from a calcium matrix that slowly dissolve to release fish food into the water. Each block lasts up to four days, making them ideal to feed your fish if you are away for a long weekend. Suitable for 12 small tropical fish or 5 medium size goldfish. Each pack contains four feeders.