We had the same problem last year so we bought a new filter the Hayward EC40AC Perflex Extended-Cycle D.E. Pool Filter this year .
Weill every time I vacuum it it looks beautiful then I shut the filter and when it comes back on almost instantly it looks like very fine sand is all over the bottom of the pool. I don't know what to do. if I leave the filter on after vacuum it's dirty and if I shut it the pool look great until the filter comes back on . Please help this is driving me crazy..