I've got a 5 yr old pool with in-floor cleaning system with cartridge filter. Normally when I put in a clean filter, the pressure gauge on the cartridge shows about 20 psi. I usually change the filter when the pressure reads between 28 & 30 psi. Last couple of times, the pressure reads about 18 psi when I put in a new filter. This time it's at 16.5 psi. I've checked the impeller and cleaned the pump filter basket. Pump seems noisier than before. I've got a clear cover on the pump filter and there does not appear to be any pump cavitation, so I'm thinking there's not an issue with suction. The pressure at the cleaning nozzles is definitely less than normal. Do pumps start to lose pressure over the year? Should I replace?