If you ever have anything in your tanks like crabs,fireworms, small fish you want out.....take a typical 20 oz plastic bottle or size to suit animal (gator aide bottle) cut top of bottle off and invert in itself. Before you do this put bait in bottom of bottle invert top and sink bottle into tank and leave. Guaranteed to catch small irritating critters. Remove all labels from bottle. neck of bottle needs to be straight inside bottom of bottle. Cheap trap that works..........