I have a problem with a gradual pressure increase in my DE filter and decrease in flow. After backflush (currently no DE in the system) the pressure starts out at 10-12psi and good flow to little over 30psi and significantly less flow over the course of 3 or 4 hours. This is repeatable because I can backflush (water is clean) and the pressure goes down initially again. The problem has come on gradually since last summer. The filter grids have been removed, cleaned and looks in good condition.
The pool and equipment is approx 4 years old and I have a Pentair FNS Plus DE Filter with a NSF valve attached.
Any suggestions are appreciated.