Pool Filters 101

By Costa Rica Pools & Construction

 Think of the pool filter as your liver….it filters all the bad elements out. When you don’t have the correct size (undersized) or choose the wrong type you will always have issues keeping your pool clean. Sand filters are good and are by far the most commonly used type of filter here in Costa Rica but there are better filters available here in Costa Rica. There are three types of pool filters, sand, cartridge and D.E. (which stands for Diatomaceous Earth).

Sand Filters:

The sand in a pool sand filter (#20 silica sand; 45 – 55 mm) is specially graded to trap particles in the 20 – 100 micron range. As a sand filter collects dirt, its efficiency increases, trapping more dirt. When your pressure gauge shows a reading 8 – 10 lbs. over the clean, start-up reading, it is time to backwash the captured dirt out of the filter.

Sand filters are known to be the lowest maintenance of the three types of pool filters. You may only need to open up the tank every 3 years or so. DE filters require removing the internal grid assembly at least annually to clean them well, and cartridge filters don’t backwash, you remove the cartridge and hose clean every so often, depending on the cartridge filter size. Sand filters are the easiest to operate and maintain.

Manufactures say that the sand inside a sand filter should be replaced after seven years. But things are much different here in Costa Rica, we are in the jungle and hardly any pools have covers to help keep debris out when not in use. So that 7 year rule changes a lot for us here in Costa Rica, we recommend anywhere from 3-5 years you change your sand some pool can go 7 years it they don’t have a lot of trees around them. Gradual loss of efficiency may be hard to notice. If your sand filter requires frequent backwashing, every week or two, the sand bed may be “mud-balled”, or it may be “channeled”. Other water balance problems may also contribute to pool filter sand deterioration, but a properly sized sand filter could go several years between sand changes.

 High amounts of bather oils can gum-up a sand bed. And just the years of a pump forcing water over the grains wears away the sharp edges of the sand. Such pool filter sand becomes more circular, and traps dirt less efficiently.

 Cartridge Filters:

Filter of choice for most spas and many smaller above ground pools, the cartridge filter is enjoying resurgence in popularity. The cartridge filter element an aquatic version of the pleated air filter in your car, traps dirt and particles of 25 – 100 microns in size. The cartridge is removed from the tank and hosed thoroughly, top to bottom, with a high pressure hose to remove dirt when the pressure gauge rises 8 – 10 lbs. above its clean reading. There is no backwash valve on a cartridge filter because today’s pool filter cartridges aren’t built for backwards flow. Instead, the pump is shut off, air bleeder opened to drain the tank, lid removed, cartridge(s) removed, hosed thoroughly top to bottom, and replaced. It’s a bit of a pain to do, but hopefully the filter is sized so that it’s a once or twice per year job.  Another advantage is that cartridge cleaning doesn’t waste as much water as backwashing. Too much pressure while cleaning may damage the cartridge, each time the cartridge filter element is cleaned; some of its filtering ability is reduced. The cartridge should be replaced every 3 – 5 yrs, depending on the work it was asked to do. If the filter was a bit undersized, and had some algae every year and lots of tree debris, etc. then it may last only 1 – 2 years. Nicely sized cartridge filters can operate for 6 months between cleanings and get more than 5 yrs from the cartridges. 

D.E. Filters:

For unsurpassed water clarity, choose a Diatomaceous Earth filters. This is the natural water polisher, Diatomaceous earth is made up of tiny fossil exoskeletons when used with a DE filter, debris as small as 5 microns are trapped, returning highly filtered water to your pool. With a DE filter you don’t backwash as often because when you do it washes out the DE element and you must add new to replace what was backwashed out. 

Remember that for sparkling water, we need the trio of: sanitation, filtration and circulation. If one of these areas is lacking, the water won’t look so good. So, if you’ve kept very good chemical maintenance and your circulation is good, you may have a filter problem. Is the filter sized properly? Many filters were grossly undersized; to save money the trend now in pool filtration is “Go Big Early.”