Clean It Up!  Facts about Pool Filters

Have you ever stared at green-tinted pool water and wondered, I’ve added chlorine and the algae remover recommended by the pool store. Why won’t this clear up? Chemical balance (see our November blog post) and filtration: one of the two holds the answer.

Filtration is essential for making pool water clean, clear, and swimmable. It’s possible you have tried to take apart the filter and clean the internals with no good, visible results in the pool. Let’s discuss the following to help you understand filtration:

  • Types of filters and their effectiveness/set-backs
  • Filter maintenance
  • Filter sizing

Decisions, Decisions…

If you do a web search for pool filter, you will need to refine your search – SO. MANY. FILTERS! Various manufacturers, sizes, and types of filters are available to the consumer, and the opinions for or against each are even more numerous. Let’s bring order to the chaos.

As we continue, know that backwashing is the process that gets rid of filtered material, typically done weekly for sand filters and every few weeks for diatomaceous earth (DE) filters. It involves a series of steps, including changing the backwash valve position and turning the filter pump on and off, that cleans much of the debris off of filter internal components. Then, at least twice a year, cleaning should be done for all but sand filters. This involves taking apart the filter, removing internal components, rinsing them, and re-assembling the filter. One more note: a micron is a unit of measurement that is .000039 inch, invisible to the naked eye. This is how we measure the filtration capability of a filter. For residential pools, here are the 3 types of filters available and factual information for each:

  1. Sand filters use sand as the medium through which water travels in order to clear small particles before the filtered water is sent back to the pool. This is perhaps the oldest type of filter, and many are still installed. Although sand filters require more frequent backwashing, you do not take apart the filter and clean out internal components semi-annually, like other types of filters. Also, there is nothing you need to add to the filter as it relates to filtration (see diatomaceous earth filters below). However, there are a few drawbacks. Sand only filters out materials larger than roughly 40 microns (this number varies study to study) and worsens the older the sand is. This means it does not clean as well as its counterparts. Also, backwashing is less efficient, meaning more clean water is sent to waste to get the filtered material out versus a DE filter. Finally, every 4-6 years (for a residential pool) the sand must be replaced, because older sand is rounder and can no longer filter small particles.
  1. Cartridge filters rely on paper or fabric cartridges as their filtration media. They can filter out materials as small as 10 microns when clean, and they have a much greater surface area than their counterparts. Under the same circumstances, a cartridge filter can allow greater water flow because of the larger total surface area. They are more efficient than sand filters, not as efficient as DE. You cannot backwash out the filtered material; cartridge filters must be taken apart every six months at a minimum and rinsed off with a hose or pressure washer. Because you do not send water to waste with these filters, the water is not refreshed as often as with sand and DE filters. This means chemical factors that do not naturally fluctuate, namely calcium hardness and cyanuric acid, will build up over time and must be removed by pumping out most of the pool’s water and refilling.
  1. Diatomaceous Earth filters are the best at cleaning your pool water. They use a filter medium consisting of fossilized diatoms that coat grids of plastic and fabric. With a micron rating of 5, they get the smallest particles possible out of your water. However, they require a little more maintenance than the other two filters. When you finish backwashing a DE filter, you must add new DE via the skimmers. They also should be taken apart twice a year, cleaned, checked for breaks, and reassembled. Diatomaceous Earth powder can irritate your respiratory system if you breathe it in relatively sizable amounts. However, like with any pool chemical, proper handling and awareness are the keys to safe and healthy pool maintenance.

Size Matters

Here’s where the square-peg-in-round-hole discussion begins, in a way. The size of your pool filter is dependent on two main factors: pool size (for the sake of fully circulating the water) and filter pump flow rate. For filters, bigger is typically better, but it all depends on how powerfully your filter pump sends water through the filter. For instance, we typically would install nothing smaller than a 48 sq ft DE filter if the filter pump is 1.5 horsepower. If your filter is too small for the pump’s flow rate, you will subject the filter to greater potential damage, which means more maintenance and repair costs. If too large, your filter will clean well but not backwash thoroughly. If your filter and its filter pump are undersized for the needs of the volume of pool water, you will not filter all of the water at least once every day.

A Well-Oiled Machine…

Hmmm…let’s keep oil out of the pool, okay?  But the metaphor is accurate. If your filter is sized properly, if you have a professional care for it regularly, and if you know the intimate details about your particular filter (including maintenance records), then it will work well for you for as long as it can withstand time and the elements. Should your filter need maintenance, repairs, or replacement, give Select Pool Services a call. Our experts know filtration and can help you with any pool/spa question or service need you may have.


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