I had something simmilar on my clowns, it came and went over the course of a week, they were super small and you really couldnt tell what they were even with a magnafiing glass. They dissapeared over night one day and I havent seen them since, I suspect they were microbubles because I hadded a new protien skimmer that week and it was still breaking in. Its been almost a month and I havent seen it ever again.