There are three primary types of filters used in the spa and pool industry:

1. SAND FILTERS which trap particles 25-30 micron;
2. CARTRIDGE FILTERS which trap particles 5-10 microns;
3. DIATOMACEOUS EARTH (DE) FILTERS which traps 1-5 microns.

Cartridges are basically the same for any sized filter. Their differences are found in the size needed to fit the individual system. Because cartridge filters cannot remove living algae from the pool or spa, the algae must first be killed. When filtering the dead algae from the pool, a flocculent or clarifier is needed. Diatomaceous earth (DE) is an excellent filter aid because of it small micron rated capacity.

How Dirt Can Help Your Pool Filter Cartridge

Although it may seem contradictory to its purpose in helping keep pool or spa water sparkling, a dirty cartridge filter is actually more efficient than a clean one. Cartridge filters used in the pool and spa industry rely almost always on a spun polyester material that allows water to pass through but traps foreign particles and dirt. The dirt builds up on the filter fibers and forms an even tighter web, thus trapping more and more particles than before. With each succeeding cycle, the openings in these filters grow smaller and smaller. By the time the water has passed through ten times, the filter cartridge will remove much smaller particles than it did the first time. Consequently, the filter's ability to trap small particles usually increases as the filter loads up. The flow rate decreases, but the dirt-trapping ability increases.

Cartridges need to be hosed off when the pump pressure rises 8-10 pounds over its normal pressure or once month, whichever comes first. They also need to be replaced every 2 years.