Existing Filter Types
There are to date only three existing filter types:
Sand filters, although the Standard, are perhaps the least efficient of available pool filters, but also the least expensive . Sand Filters are big tanks that hold special pool sand. As the dirty water filters through the mass of sand, the sand's sharp edges snag the dirt.
Sand filters can remove dirt particles down to about 30 microns (new sand) which is efficient enough to keep most pools clean. Old sand (even 6 months) or heavy loads (the pool suddenly turns green, or gets a lot of dirt) will generally be too much for the filter to cope with.
Maintenance can be tedious. In order to clean them (they need cleaning about once a week), you need to backwash. Backwashing is when the water flow is reversed and clean water washes through the filter. This water is ultimately wasted . Sand filters are not a good choice where there are water restrictions.
- Diatomaceous Earth Filters
Diatomaceous Earth is a powder made of billions and billions of fossilized plankton skeletons. The inside of a Diatomaceous Earth (D.E.) filter holds a number of cartridges coated with the stuff. It works very well to catch and hold dirt. They are the most expensive type of pool filter, and they get the pool water cleaner than any of the other existing filters. D.E. filters can trap particles as small as 3 microns.
Maintenance, however, can be demanding. Most of them require backwashing, and this isn't always enough to get them clean. You may have to remove the grids, and manually discard the D.E.
D.E. Filters, although very popular at one stage, have progressively been phased out, and today are a rarity in the swimming pool environment.
A cartridge filter is a tank that holds 3 or 4 cylindrical cartridges. Each cartridge is made up of a fabric like polyester that catches the tiny particles of dirt until you clean the filter.
Cartridge filters can handle dirt as small as 10 microns (the naked eye will detect about 45 microns). Cartridge filters are usually less expensive than diatomaceous earth filters, but more than sand filters.
Cartridge filters require very little maintenance. You can sometimes get away with just hosing off the cartridges a few times a season. You may need a cleaning solution, or a replacement cartridge, which is generally inexpensive.
Due to the relative unavailability of replacement cartridges, however, these filters are seldom used in some swimming pool markets.