I see them in all my skimmers never thought anything of them , never seen anything come from them so I just never pay no mind , but now looking in my skimmers there seems to be a bunch of snails that shouldn't be , they have no way to get were they are at so they must have been egg sacks , 2x a year I do have snail populations grow tons of baby nerites , but that's always after I replenish the snails many say snails surviving reproduction in a closed system is 0 to nill I disagree I always see baby snails and they seem to survive, couldn't say 100% those sacks are eggs but looking into my skimmers now really makes me wonder