I have been sweeping the bottom of my pool and my PSI has been going uo about 10 PSI before sweeping is not longer effective. This is what I would expect. What is strange is that when I backwash the filter the water leaving does not look dirty at all. The pressure does drop. I did just get done rebuilding my multi-port value also. In the past I've always had very dirty looking water when backwashing. Should I be concerned.