I got lazy and let all four sides of my tank get covered in coraline, so tonight I was scraping the glass and around the bottom where the coraline dust was accumulating there were hundreds of these snails. They are so small I had to get a magnifying glass to view them, from a distance they just look like substrate but if you get close enough there are a bunch of them. They are about 1/8 to 1/4 of an inch long and look like solid white cerith snails, but I have heard of pyramid snails and some snails that eat clams that look like tiny ceriths. I have some ceriths in my tank and refugium but they are not white. Let me know what you think these are.