Just like it says....
I essentially have the same setup - pump,filter etc with no changes for several years now without any problems. My pool is commercial, 33k gallons.
I typically only have to backwash every 4/5 weeks depending on pool use. Normal running pressure on the Pentair 60sq ft DE filter gauge is 17 PSI.
Lately, I can't go 5 days without the pressure building up past 30 PSI. Both of my return lines are blowing bubbles into the pool when the pressure rises also. I first swapped in a new quality PSI gauge without luck so the gauge is reading correct.
Another issue that's occurring is I'm also getting DE past the filter and into the pool. I carefully inspected each grid- no holes, tears or broken plastic pieces found.
After a thorough cleaning, I returned the pool to service and made it about 5 days before having to backwash yet again.
I then through my hands up and purchased ALL new grids and replaced the top manifold. Again, the pressure rose to above 30psi within a few days after a complete filter rebuild and I'm still getting DE in the pool.
I'm at a loss and have NO clue as to what to check next. I've been maintaining this same pool for over 9 years and this has me stumped.