I have been vacuming and vacuming but I can't seem to get the green stuff to go away. It will go away for a few days, but then it will come back slowly over time like 3-7 days or so. The water is clear however the bottom of the pool has green stuff that if you disturb it wil cloud up. I believe that once a vacume it up it is just coming back through my filter and into the pool. Please help.