28,000 in-ground pool. I have a Pentair 4000 with 8 grids. After adding one half an orange pitcher of DE the filter pressure will rise by 50% within a few hours to 30 on the gauge. Normal without DE is 18. I can run the filter for weeks without DE and the pressure does not increase much. Backwashing after DE is in the system drops the pressure back to the normal value of 18 but it quickly rises to 30 which is high. Will getting new grids correct the situation and allow backwashing to get rid of the DE to the street? The grids are probably 8-10 years old or older as I bought them used not knowing what I was doing back then. The attached photos show one grid that I have half sprayed off and the other is before any spraying. Thanks.