So I was cleaning the coarse filter I have over the end of my skimmer to stop fish and such from getting sucked in, and I noticed these really hard white things bound in the meshing. I tore a small piece off and pulled out the items. They are tiny little snail shells. They had the opening and everything, I was unable to see any snails, but I am sure they were new shells. A week and a half ago, my 2 big astrea snails sat and spewed white stuff into the tank for about an hour, and I turned off the flow to let them mix. Really neat. I freed a couple from the meshing, and hope they thrive. The other ones were to tightly bound. I may go buy a new cover tomorrow and cut the other one up.