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Comparing Swimming Pool Filters

The Water Quality Triad

Water quality depends on three things working well: Circulation, Filtration, Chemistry. Ideal water quality requires all three of these, and they are interdependent. Filtration is only as good as the amount of water that passes through it. The same can be said for secondary systems for disinfection and oxidation.

Types of swimming pool filters

There three primary types of swimming pool filters: sand, cartridge, and D.E..

Sand Filters

Pressure sand filters are sealed vessels full of filter sand and gravel. Recently, a new type of filter media, crushed glass, has become popular to take the place of sand. Most sand filters are pressure sand, where water is pumped into the top of the sealed filter, and the water pressure pushes water down through the depths of sand and gravel (or glass), and eventually out through the bottom, through openings called laterals. Pressure sand is probably the most common filter in the commercial swimming pool industry. Vacuum sand filters are exclusively a commercial pool product, and can also serve as a surge tank. Rather than pushing water through sand and down through laterals, vacuum sand filters pull water down through the sand. Just like pressure sand filters, vac-sand filters can also use crushed glass media.

Pros and Cons for Sand Filters

These are usually the most affordable type of filter to purchase and and maintain. They are also easy to clean out particulates to waste. The cleaning cycle is called backwashing, which is when the operator reverses the direction of waterflow. Water pumps up from the bottom of the sand bed, and out the top to a waste line. Because of the ease of backwashing, maintaining sand filters is pretty straight forward and easy. Pros:Affordable, easy to clean (backwashing), simple to use, and they last a very long time. Cons:sand filters capture particles as small as 20-30 microns (µ), which means their filter screening ability is the weakest of all types of pool filters. Smaller particles can pass through the filter. The problem isnt that sand wears down, it's that it gets fouled by years and years of contamination. It just needs to be cleaned and freed from the oils and 'body butter' that have made it disgusting.

Cartridge Filters

Cartridge filters are very rarely used in commercial pools. They are common in residential pools with low bather loads, and their screening ability is better than that of a sand filter (down to 8-12µ particle size can be captured). But while clarity might be better for a while, cartidges tend to get dirty faster, and need to be cleaned. Unlike sand filters with a simple backwash function, cartridge filters must be opened, removed and manually cleaned. It takes time and effort, and it is not a fun job. On top of that, cartridges do not last very long compared to sand. Some need to be replaced more than once a year, depending on how the pool is used and maintained. Pros:Simple installation, easy to use, good water clarity. Cons:Laborous to clean (and the cartridges must be cleaned frequently), and their longevity before replacement cartridges is low.

Diatomaceous Earth (D.E.) Filters

D.E. Filterscan capture particles as small as one micron (1µ). These filters have the best screening ability of any pool filter. Residential D.E. filters use a series of grids, similar to that of a cartridge filter. The difference is, the grids themselves need to be charged or coated with a powdered media called diatomaceous earth, or alternatively, perlite. The D.E. or perlite media is pulled into the filter through the skimmer, and coats the outside of the grids. The grids + media become the screening filter that captures just about anything and everything. Commercial D.E. Filters are the most advanced, automated filters in the aquatic industry. These are the filters that the best aquatic venues and water parks are using. They automatically regenerate a fresh layer of perlite through a timed "bump" cycle, hence the name Regenerative D.E. Filter. Both residential and commerical D.E. filters have to change out their media periodically, depending on the bather load and pressure that has built up. Pros:The best screening ability (by far), [commercial] regenerative cycle is automated, optimal water clarity. Cons:Most expensive filtration, periodic media dumps/replacements, and while they are automated, they are also more complicated to operate.

Conclusion

Does the type of filter really matter? Yes. Are the differences between pool filters even noticeable? Over time, yes. It depends on how often you use the pool and how well you're paying attention to the water clarity. How do filters impact water quality? Their screening ability determines the size of particles each filter can capture, which has a direct relationship to water clarity and water quality. Does filter type have any affect on indoor air quality? This is hard to say, because chloramine production is about the removal of nitrogen and organic compounds by chlorine, which are small enough to pass through filtration. Pools with all types of filters have chloramine problems. Then again, less contaminants circulating can reduce chlorine's burden, so perhaps there is somewhat of a correlation. Hopefully this article helped explain the three types of swimming pool filtration.