I have a Hayward DE 6020 with a Hayward Selecta-Flo Valuve. It has four settings; filter, waste, backwash and pool or spa boost. After I backwash, add new DE and turn vaulve back to filter, powder and debris shoot out of returns for a few seconds and we end up wih a little pile of DE and debris in the bottom of the spa. All the instructions I find for backwashing say to use rinse setting after backwashing but mine doesn't have one. I have checked for holes and rips in filter but don't see any. Tag on the side of my filter says I should use 7 .5 lbs of DE and I am using a scoop made specifically for DE. What am I doing wrong?