Why forced backwashed, but waste water is clear

[LukeChi]

My sand filter is TRITON TR60 (non ClearPro).

I changed the sand and put in 275 lbs. of QUIKRETE Pool Filter Sand #1153 bought from Home Depot and 50 lbs bought from Leslie's yesterday. The eight laterals were checked and they were in good shape. The "X" Free Board was 10.5 inches as what the manufactures suggested.

After the sand replacement, I did the backwash to wash the new sand. But, I, then, started to be forced to backwash the filter almost every 2 to 3 hours due to the low water flow into the swimming pool and the high pressure of the filter. I noticed that the water removed from the filter due to the backwash was not dirty at all. It actually was not needed to do the backwash when the water flow into the swimming pool was slow and the pressure of the filter was high.

After I did the backwash, the flow of water went back to normal for around 2-3 hours and I was forced again to do the backwash again.

Thanks for the help.