I have been using solar heating successfully for years, and installed new panels in late April last year after replacing original DE filter with a cartridge filter. Heating worked well all last summer and up until recently. But for the last month or so the water entering the pool is not as warm as previously (my wife says its tepid and she's right as usual). We have no thermometer in the line going from the pump to the pool (the solar heated water blasted it off scale once and it never recovered so I removed it). Air temperature the last couple of days was about 98-99 deg F. Today it is 97 deg and the pool temp is 82 and the water coming into the pool from the solar panels is at about the same temp. I "cleaned" the year-old filter cartridge today, and have been cleaning it about every two months with a cleaning wand attached to a hose. Another symptom is that there is a lot of air coming into the pool from the two inlets (more from the farthest inlet from the pump). One possibility is that ash from recent forest fires accumulated on the panels; the panels were hosed off (from ground level, it is a one-story house), but maybe this wasn't sufficient.
Questions: Where could the air coming from? Could the year-old cartridge be the problem and need replacing? What is the best way to clean cartridges? Any and all suggestions will be appreciated.