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Choosing the Right Pool Filter

Cartridge, Sand, or Diatomaceous Earth? Check out our guide to selecting the perfect filter for your pool

If you’re new to the world of pools, the multitude of options for nearly everything can seem overwhelming. Fortunately, however, when it comes to pool filters your choice is going to be an easy one! Simply follow this formula: Pick the one you like. Yup, you read that right. Practically speaking, they are all pretty much interchangeable; there is nothing one type of filter can do that another can not.

There are minor differences, however. Mostly to do with maintenance, but also ever-so-slight performance differences. Let’s go over it!

Cartridge Filters

Hayward Swimclear Cartridge Filter
Filter shown: Hayward Swimclear

While they are the go-to filter for smaller bodies of water (such as spas and aboveground pools), cartridge filters are also perfectly suitable for larger in ground pools. As the name implies, a cartridge filter contains a replaceable cartridge that provides the filtration (sometimes several cartridges, as in the case of the Hayward Swimclear, for example).

Replace the cartridge!? How often, and how much does that cost? Not so expensive, and not so often. The cartridge in a properly sized cartridge filter can last for a couple years before needing replacement. As for the cost, it all depends on the size of your filter. Filters range in the neighborhood of $50.00 to $300.00. Also keep in mind that in addition to the occasional replacement, a filter cartridge will need to be removed from the filter housing and cleaned periodically. How often depends on how much you use your pool, but plan on taking the cartridge out and hosing it off every couple weeks.

Cartridge Filter Pros & Cons

  • Filters down to 10 microns
  • Operates at a low pressure,
    which saves energy costs at the pump
  • No backwashing means a cartridge filter does not waste water
  • Not suitable for very large pools
  • Cartridges need to be replaced

Sand Filters

Pentair Sand Dollar Sand Filter
Filter shown: Pentair Tagelus

Sand filters operate by passing pool water through a chamber of specially made pool filter sand. As water passes through, particles as small as 20 microns are trapped in the sand. As a sand filter operates, however, more and more debris will accumulate in the sand. This gunk buildup will make filtration less effective and increase the pressure of your filter (making your pump work harder to do the same job). It is for these reasons that a sand filter must be periodically “backwashed” to clean it out.

Backwashing involves turning the valve of your filter to the backwash position and running water through the filter, exiting via a waste hose. Once the water exiting the sand filter is clean, backwashing is complete and your filter is ready for duty again. Keep in mind that you will need a place for all this water to go. Typically, a sand filter owner will run waste water right to their yard and let the ground soak it up. How much water it takes to backwash depends on your pool size and how dirty your filter is. As an example, an Olympic-sized pool results in the loss of about 6,300 gallons per backwash cycle. Granted, most of us don’t have 660,000 gallon pools in our backyards, but plan on losing at least a half inch of water when you backwash.

In addition to backwashing, the sand in a sand filter will need to be replaced every 5 years or so.

Sand Filter Pros & Cons

  • Low up-front cost
  • Sand lasts longer than a filter cartridge
  • Ease of maintenance
  • Backwashing will lower your water level and potentially throw your water chemistry off balance
  • Sand media can weigh several hundred pounds, and will need to be replaced
  • Effective to 20 microns, a sand filter does not filter as finely as a cartridge filter

Diatomaceous Earth Filters

Pentair Sand Dollar Sand Filter
Filter shown: Sta-Rite System 3 DE Filter

A D.E. filter can be thought of as a hybrid between a sand and a cartridge filter. Inside a D.E. filter you will find a series of cartridge grids (much like a cartridge filter), and a loose filter media (much like a sand filter). The difference is that instead of using sand, a D.E. filter uses (you guessed it) diatomaceous earth! D.E. powder is an extremely fine substance which is capable of trapping particles as small as 5 microns. To put that in perspective, a grain of beach sand is in the neighborhood of 40 microns.

Regular maintenance on a D.E. filter is similar to that of a sand filter, with one caveat. Every time you backwash a D.E. filter, you are flushing the diatomaceous earth inside the filter as waste. Many localities do not allow backwashing a D.E. filter to the ground for this reason. “Recharging” your filter with fresh DE after each backwash is another cost to consider. This is done by adding the powder directly to your skimmer, where it will be pulled back into the filter and latch on to the internal filter grids.

Diatomaceous Earth Filter Pros & Cons

  • At an effective filtration of 5 microns, a D.E. filter offers unparalleled water quality
  • Backwashing will lower your water level and potentially throw your water chemistry off balance
  • Diatomaceous earth must be constantly replaced
  • Many localities do not allow backwashing a DE filter to ground

Conclusion

There is no “correct” solution to filter your pool. For the most part, our customers choose their filters based on whichever maintenance schedule suits their lives and personal preferences.
Pick the one that sounds like the least hassle so you can focus on having fun and enjoying your pool! That’s what it’s all about, right?
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