I have a Hayward Sand Filter on a 20 by 40, 27K gallon pool. After returning from vacation we had a Algae outbreak that is mostly contained now, however, when vaccuuming the dead algae up from the bottom, it appears the dirty water is coming right back into the pool through the jets. I've replaced the sand, the Multiport and spider gasket in an effort to solve it with no luck as of yet. Any ideas, suggestions? Thanks in advance.