Pool filters are primarily tasked with the purification of pool water through filtration. Filters clarify water by removing particulate matter suspended in the water.
All conventional filters, simply stated, work by passing water through some type of filter media. The biggest distinctions between the different types of filters are the size of the particle it can remove and the media it uses to achieve it.
The three different types of filters used for swimming pools are diatomaceous earth (D.E), cartridge, and sand. The type of filter you should use is determined by the landscaping, setting the pool is located in and geographical location. The size of the filter is determined by a number of factors including the volume of water, the size of the pump and the desired turnover.
As with most things mechanical there are pros and cons, better and worse. Even though some of the points are subjective to the user, there exist real world realities that someone should be made aware of when considering the purchase of an expensive piece of equipment.
In the Austin, Texas metro area the best performing filter is a D.E filter or diatomaceous earth filter due to the tremendous amount of pollen released by the bordering hill country and drought conditions we suffer every summer. Add to that, the fact that most neighborhoods have Live Oaks and Cedars, the choice becomes obvious. D.E filters have the capacity of filtering particulate as small as 4 microns. For reference, a human hair is 70 microns across. Pollen and spores can be as small as 9 microns and dust particles can be smaller than that.
A D.E filter has the ability to filter particles that require magnification to see, which gives pool water a polished sheen. This ability dramatically cuts downtime by effectively and efficiently filtering a heavily used pool or after a bad storm.
On the other hand, because a D.E filter does its job so well, it does require more maintenance and service. A D.E filter should be backwashed and recharged with D.E powder as needed; usually every 4 to 6 weeks during the swim season to prevent the powder from becoming too compressed which in turn could damage the filter grids. Additionally, a D.E filter does require a D.E filter service performed every year. A D.E filter service is a complete breakdown of all internal components to remove and clean out compressed material and to inspect and replace anything torn or broken.
A cartridge filter is the second most effective, in terms of filtering power, as its ability to remove particles is limited to particles greater than 15 microns. A large percentage of the particulate in the Austin area is made up of particles smaller than its effective filtering ability. The use of a clarifier will be required to help with the finer particles.
The best possible application for a cartridge filter is when used with a salt pool. A salt pool has a chlorine generator that produces chlorine through electrolysis. It stands to reason that you would not want to backwash out your salt since it should be maintained within a specific range. The pairing of a cartridge filter with a salt pool system is the closest you will come to achieve the idea of perpetual chlorine presence.
Since a cartridge filter does not have a multiport valve, it does not have the ability to clean itself or the ability to waste water. A cartridge filter has only one setting (filter) and requires a complete breakdown in order to clean. The task of cleaning a cartridge filter should be done every quarter or 10 psi (per gauge) and can take upwards of one hour. If the elements require a soak, it could take longer. The elements should be replaced every couple of years and can cost $70-$100 each.
Another con and reality of a cartridge filter is that it will inevitably raise the presence of everything water soluble or total dissolved solids. The total dissolved solids include salts, calcium and other minerals, stabilizer and metals. This occurs because it lacks the ability to use pool water to clean itself or the ability to periodically waste water directly out of the pool system to reduce the levels. The end result is an over stabilized pool with very hard water that is difficult to balance and sanitize.
A sand filter has the ability to remove particulate with a size range of 25 to 50 microns, thus making it the least effective filter in the Austin metro area. Its reduced filtering ability requires heavy use of clarifiers to assist in the filtration process. Along with the use of clarifiers, occasional flocculation is necessary to turn a pool around.
Sand filters are often chosen because they are easy to use and require little maintenance. When a sand filter is backwashed it does not need to be recharged and does not require an annual service. Unlike a cartridge filter it is self cleaning, which means you don’t have to spend hours cleaning the elements with a garden hose and then struggle to get the tank to seal.
The sand bed in the filter starts off very coarse and textured. This texture gives the sand bed the ability of trapping suspended particulate. Once a filter is employed, the constant agitation of the sand bed begins to polish the individual sand grains. When the individual sand grains lose their texture they effectively lose their filtering ability.
Filter sand should be changed out every 3 to 5 years due to the polishing that occurs during regular use. If the pool chemistry is out of range, the sand bed could harden due to calcium and cause channeling, which will cause the filter to become ineffective. Finally, every time the filter is backwashed, you lose a small amount of the finer grains. When the finer grains are lost you are left with only the larger polished grains which will not be effective in filtering particulate.
To summarize, all filters will help remove suspended particulate introduced into a pool. A D.E filter is the most effective and efficient in achieving this task in Austin, TX. The next would be a cartridge filter, and lastly a sand filter. Even though there is more maintenance needed for a D.E filter, the pool always looks beautiful and is ready to use.
When purchasing a filter of any type the manufacture order you should obey for quality is Jandy, Pentair, Hayward, and then everyone else.