My DE filter runs about 22psi when it is clean. I backwash around 30psi.
I had a problem when the system was new where the filter grids got covered with plaster paste. I didn't know this was happening. I backflushed quite often (for a week or so) and the pressure would return to normal after each cleaning but quickly get back uo to 25 -30psi within a day or so. Finally I disassembeld the filter and found the plaster paste all over the gids. The backwashing was not cleaning the grids thoroughly. After I washed the grids clean (done without removing grids) with a garden hose the problem never returned. I was just a new pool start up problem.
I don't know if this helps or not.
Good luck