All filters need to be cleaned out periodically. How often a filter will need to be cleaned out will depend on the type, size and age of your filter, and the general condition of the pool.
Under optimal conditions the sand in a Sand Filter should be changed every 5 – 7 years, a Diatomaceous Earth filter should be “Acid Washed” every 2 – 4 years, and Cartridge filters needs to be cleaned every 3 – 6 months.
Cartridge and Diatomaceous Earth filters are much more prone to clogging up, as a result they will need to be cleaned more often. If you are clearing a green pool with anything other than a Sand Filter you should clean the filter after you have cleared the pool. In fact a Cartridge Filter may need to be a few times while clearing a green pool.