They are for spare if you can't breed brine shrimps on time or your mother just forget what are they or throw it away because they just look like sand in the water. You know, kids playing sand in the beach. Raise your own brine shrimps and it is cheaper. The frys love to catch something that is moving. Also you want them to exercise rather than sitting at the bottom become fat and let the bateria or fungus to eat them up.