Sand filters should be cleaned at least once per season, preferably in the fall before closing. You must clean your sand filter after encountering bouts of algae.
When should a cartridge element be cleaned?
For swimming pools, clean the cartridge when filter canister pressure reaches 8 PSI above the initial system or new cartridge starting pressure. For spas, establish a routine cartridge cleaning schedule based on the amount of spa usage (this should include rinsing the cartridge weekly, as well as using Filter Cleanse every 4-6 weeks).