I have a Hayward cartridge filter. I just did my first cleaning, the filters were very dirty, lots of sand etc., I cleaned them very well, soaked overnight in TSP, then cleaned/rinsed again, there was piles of sand/debri after cleaning, they were a completely differnt color. My question is, my system was running right at 20psi prior to cleaning, and is still running the same after cleaning. I as expecting a substantial drop after all that. Is there something else I should be doing? The cartridges appear to be very clean now.