I had clear water yesterday and today. Last night I forgot to override the timer and it was off till 100pm this afternoon. The pool is still clear with deep purple on the test strip.

At 300pm, the pool floor was clean. Tonight at 800pm, the pool is accumulating yellow-green dust again. the test strip is still deep purple for FC.

I backwashed the filter even though it was at its normal 18 psi. I the backwash was green and dusty in the sight glass.

I have not purchased any DE. I think that it might be time to open up the filter. There is a leak at the flange clamp. It is leaking water on the backwash and there is a hissing sound when in the filter mode.

Assuming that the filter is 10-15 years old........we have been here 7 years. what is the best course of action at this point?

Add the DE and see if its blowing through or just open up the filter?
Dig out the sand?
Replace the sand? Add more sand? Or just add the DE to the existing?
Pull out the lateral assembly while I have it open?