I forgot to add that the stuff reappears within minutes sometimes. I think I have a filter problem and would like some opinions before I go spend major $$ on a replacement part.

What is a spider gasket - what does it do and do I possibly need one? All sand was replaced about a month ago and all the laterals thoroughly cleaned. The sand had a layer of grayish gunk on it that would not backwash out - all backwashing this year has been clear which I find very strange.