It’s summer, which means the number of swimming pool permits has skyrocketed. In previous years, pools were simple, rounded-or rectangular-shaped concrete lagoons that graded from shallow to deep.  Nowadays, pool installers are building Sea World in people’s backyards. But with all the focus on fantastic design and innovative materials, it’s easy to overlook one critical decision that pool builders have always wrestled with: filtration. Choosing the right filtration system is essential to keeping your pool healthy and clean.

The most common pool filter is the sand filter. It is easy to maintain, inexpensive to replace, and it lasts seven years before it has to be changed out. On the other hand, it requires weekly or bi-weekly backwashing to keep the filter clean, and backwash valves are probably the most inefficient pieces of equipment in a swimming pool system and often have leaks. Another problem with weekly backwashing is that it can throw your pool’s pH off-balance. Although it is more cost-effective in the long-term, sand is the least effective filtration method because it only catches particles that are 20 microns or larger. Sand filters are best for larger pools that receive moderately frequent use by a family of five or smaller.

Diatomaceous earth (DE) is a fine powder made from the exoskeletons of fossilized diatoms, which were hard-shelled algae that lived during the Pleistocene era. DE filters are composed of grids coated with DE powder which the pool water is washed through. The DE coating catches all the debris and particulate matter. DE filters are cleaned on a weekly basis and a bit more DE powder is added with each cleaning to “recharge” cleansing system. For best results, the DE filter should be totally disassembled, hosed off, and recharged with fresh powder each season. The DE filtration system is more expensive and time-consuming than sand and cartridge filtration, but it filters particles of 2-3 microns in size and results in superior water clarity. DE systems are best for larger groups, families the swim frequently, and night swimming. The superior water clarity is easier to appreciate when the pool lights are on.

Cartridge filters are the second most common pool filters. The cartridge filter works an awful lot like the water filters that people attach to their kitchen sinks. The average cartridge filter is between 100 and 300 square feet, so they have a huge filtration surface area. As a result, cartridge filters don’t get clogged as often as sand filters and require less water pressure to work. Some cartridge filters are made of inexpensive materials and meant to last only two or three seasons, but the higher-end filters can last up to five seasons.  Cleanup is a cinch because instead of backwashing, the filter is just taken out and hosed off once or twice per season. Cartridge filters clear out debris of 5-10 microns in size. Cartridge filters can handle a larger volume of frequent swimmers than sand filters and are good for those who entertain often. The larger the pool is, the more cartridges are needed to keep it clean. In places where sand and DE are outlawed, cartridge filters are the only option.

Knowing how frequently the pool will be used, how effective the filtration needs to be, what the filter’s maintenance needs are, how much real estate homeowners want taken up on the pool’s equipment pad are the key considerations for choosing a pool filter. As soon as that’s decided, pool builders can get back to the bigger concern: creating a backyard paradise for their clients’ enjoyment.