Just fyi, they don't lay eggs in your tank. They brood their young inside their shells and release live young at the water surface at night. Usually several at a time. They are so tiny they can float on the water tension, until they find something to cling to. They are voracious algae eaters, thus useful where algae is a problem, and do keep detritus levels down. Personally I would not have a tank without them, though if I ever had space for a real show tank, I'd not want too many of them in it.