Your filter is the kidney of the pool. Every gallon passes through it, and everything it catches, from dirt and pollen to sunscreen oils and dead algae, stays there until someone cleans it out. Over a few months, that buildup cuts flow, raises pressure, and leaves the water looking dull even when the chemistry is right.
The easiest thing to watch is the pressure gauge. Note the reading right after a cleaning. When the needle climbs about 8 to 10 PSI above that number, the filter is due. Waiting longer makes the pump strain, costs more in electricity, and shortens the life of the motor and seals.
Cartridge filters need their cartridges pulled and hosed pleat by pleat, with an occasional degreasing soak. DE filters need a full teardown so the grids can be cleaned and checked for tears, then fresh DE added. A quick backwash is not the same as a proper cleaning.
Most residential pools in the Valley need a full filter cleaning two to four times a year, more often after a green clean-up or heavy use. It's one of the most cost-effective things you can do for your water and your equipment.