I have noticed this year that every few days there is a very small amount of fine sand on the bottom of the pool. It appears to accumulate just in the creases on the bottom. I clean completely, then a couple days go by and the sand is there again. It is so fine that if you wave your hand or foot by it, it just disapates....so it is very fine. I have put a cloth around the jet and I do not see any sand being blown into pool. Could this be a faulty sand filter? (1yr old) Or is this just dust from the air getting in the pool? Any things I can check without draining filter/sand? Any ideas? Thanks!