Diatomaceous Earth (D.E. Filter) - basically this filter type uses D.E. to filter out the dirt, bacteria, and viruses. It is the best filtration, down to 5 Microns. This video covers everything you need to know about the D.E. filtration system.
If you want to learn how to clean a specific D.E. filter, learn more about backwashing and to see all of my videos on D.E. filters click on this button here:
D.E. Filters are the most common filter type in my area so I will touch on these filters first. D.E. Filters or Diatomaceous Earth Filters offer the best filtration of the three types. They use a set of grids or cartridges depending on the filter type and a coating of D.E. Powder (Diatomaceous Earth). The D.E. coats the grids and acts as a barrier trapping dirt, debris, algae, and organic particles. This allows a D.E. Filter to filter down to an amazingly low 3 microns.
A little about what a micron is for you:
A "micron" is an abbreviated term for "micrometer", or a millionth of a meter (1/1,000,000 meters). This is about .00004 inches. For Size comparison, a human red blood cell is about 5 microns across. A human hair is about 75 microns across (depending on the person).
So a micron is a very small measurement and a D.E. Filter will give you the best water quality of the three filter types.
Another benefit of a D.E. Filter is that the design allows for a very small amount of filter sq ft area to keep your pool crystal clear. Typical D.E. Filter sizes are 36 sq ft, 48 sq ft, 60 sq ft, and 72 sq ft (they also make a 100 sq ft Quad D.E. Filter). So you can easily get away with using a 48 sq ft D.E. Filter on a 20,000-gallon pool. So don't let the smaller sq ft size fool you into thinking that a D.E. Filter is inferior to say a 200 sq ft Cartridge filter or a 300 lb Sand Filter. The D.E. Filter just utilizes the sq ft of filtration area much more effectively with the coating of D.E. on the grids (or cartridges in the case of a Quad D.E. Filter).
Another benefit is the ability to backwash a D.E. Filter in between cleaning it. This is a process in which the water flow is reversed forcing water inside the grids and pushing dirt and algae off of the grids and out the backwash pipe. Convenient if the pool gets a lot of dirt and use each season.
The drawback of D.E. Filter is that they can be messy to take apart and clean, especially if your backyard is all cement. The old D.E. powder can linger for months. They can also be challenging to take apart and clean. Many cities require it to be plumbed to a P-Trap or ban them entirely.