in my tank i have these small snail about a 1/16" and smaller they like to hang out on the glass and eat the alge their. they are cone shaped with small black bands on them. they arent a spawn from existing snails because they just showed up by the hundereds in my fish only tank which has no snails in it. i think they came with the live sand as i did not see them before that. anybody got a clue?