The pump is 2 HP and the main plumbing is all 2". The plumber that installed the pool said that was required since I have a large pool/hot tub combination. The pool has 2 skimmers, 5 returns...the cleaner is a suction cleaner. There is a heater in line but most of the time water is not diverted to the heater, it is mostly used for hot tub which has 6 jets and 2 returns to the hot tub.

One way that I could see this happening is running the hot tub only when the filters were dirty, we did that this winter a couple of times. It was always done at night and I wasn't paying much attention to pressure. But if it holds true with the 10 psi increase I usually have when filters get dirty, it could have been in the 35 psi range.

Under normal conditions when the pool returns are run the filter runs at ~12 psi. When using the hot tub only it runs at ~25 psi. As part of trouble shooting this, which I have done twice now, I tried using the different returns to test for clogs, etc. At first it all seems to work normally, none of the settings seem to increase pressure any more than normal such that it would indicate a problem in the line. As time goes on it always increases slowly, about 1/2 psi per minute until it gets up to 32-34 psi which it stays at until I clean the filters again.

The filters are ~2 years old, they look to be in pretty good condition. I generally clean them every 2 months normally, more often (every month) during the 3 months of heavy use and when the dog is shedding. Only 1 of the 4 filters has a frayed looking section on it. Do they make generic cartridges for these things? The local pool store and most of what I am finding only carry the very expensive Hayward branded ones.