Can anyone tell my why green water just came out of the filter into my pool? My husband and I just bought a new Hayward filter for our above ground pool coz the last one broke.  We shock the pool and vacuum all the dead algae in the bottom.  When he turned the knob back to filter, all these green stuff went back in to the pool and made the water green again.  I checked on it this morning and i can see the bottom of my pool is green.  Also, when ge did backwash, sand starts to come out aswell.. lots of it