Here are some pictures of some pool filters before and after cleaning that show you why you need to have your pool filters cleaned every 4-6 months. Some of the pictures are DE Pool Filters and others are of Cartridge Pool Filters. 

The swimming pool filter catches all the dirt and grime from your pool and it sticks in your filter. Your clean pool water runs through this filter before returning water to the pool. Do you want your pool water running through this collection of dirt, bacteria, and algae?

Another reason you need to clean your pool filter is that a dirty pool filter cannot run effieciently causing higher electric bills, wearing out your pool equipment faster and causing more swimming pool repairs. 

Proper pool filter cleaning and maintenance at regularly scheduled invervals (see below) will keep your pool water cleaner, your pool bills lower, and your pool equipment will need less repairs and will last longer.

Clean your cartridge pool filters every 4-6 months. There is no way to "backwash" a cartridge pool filter, therefore it's imperative you remove the pool filter and CLEAN it every 4-6 months.

DE Pool Fitlers should be Backwashed as needed (when pressure gauge rises 7-10 psi above its "normal level"). Inspect and clean your DE filter grids every 6 months

Sand Pool Filters should be backwashed as needed. Change the sand in your sand pool filter every 3-5 years.

***Backwashing is the term used for reversing the flow of water through the filter to flush out the dirt and debris that has collected in the filter.