A properly sized swimming pool filter is the first and most important step to maintaining clean and clear pool water. Pool filters remove dirt and debris which allows chlorine, bromine or other sanitizer to focus on destroying bacteria.
Check sizing recommendations on whatever filter type you choose, and always go bigger if you can afford it – an undersized filter will just not be effective. It is always better to buy a larger filter than you need, especially if you are on the edge between two sizes.
There are 3 kinds of pool filters: Sand, Cartridge and DE (which stands for diatomaceous earth). All three are very capable of properly maintaining the water; there is no one best pool filter for all applications, but many owners do have a preference for one over the other. This will help you decide which pool filter type is best for you.
Sand filters are the oldest and most common type of pool filter. The filter tank is filled with a specific grade of sand called #20 silica sand, which is available at most local hardware stores, or sand and gravel yards.
Water enters the tank and is pushed down through the sand, which traps dirt and debris. The water travels all the way down to the bottom of the tank where it enters the laterals and then is returned back into the pool.
In the cutaway image you can see the laterals at the bottom of the tank. Water filters through these slotted pipes, and then goes up the center pipe to be returned to the pool.
Sand filters are capable of filtering particles about 20-40 microns in size, which technically makes them the least effective amongst the three pool filter types in terms of the particle size removed. They are the easiest to maintain, requiring backwashing or cleaning to remove dirt from the filter when the pressure gauge has a reading of 8-10 psi over the start up reading.
Eventually backwashing will no longer be able to remove the buildup, and the sand particles will become smooth and unable to trap debris, and the sand will need to be replaced. On average this is required about every 5-7 years, but can be much sooner for undersized sand filters. The sand probably needs to be replaced when more frequent backwashing is required and it is difficult to maintain filter pressure at a normal level, or clear up pool water problems. For details on filter sand replacement, check out my blog post “How to Change Pool Filter Sand”.
Sand filters are available for any pool size, and they are generally the only filter type you’ll find in large commercial applications.
Cartridge filters are so named because they contain a pleated spun polyester filter cartridge that looks similar to the air filter you will find in your car. Water is forced through the cartridge pleats and it will trap debris as small as 5-25 microns, a significant improvement over sand filters.
Cartridge filters require very low maintenance. An over-sized cartridge filter only needs to be cleaned about every 6 months, or whenever the filter pressure is 8-10 psi over the standard reading.
Each time a pool cartridge is cleaned some of its filtering ability is lost, and eventually oils and debris will build up to the point that they cannot be removed, so cartridges do need to be replaced, usually every 3-5 years.
Replacement pool filter cartridges vary in price, but on average, new pool cartridges are in the $30-$100 range, for each cartridge. Some filters may have several cartridges. For more details on pool cartridge cleaning and replacement, check out my blog post “Pool Filter Cartridges: When to Clean and When to Replace”.
DE Pool Filters
D.E., or Diatomaceous Earth filters remove particles down to 1-3 microns in size, a smaller particle size than can be seen by the naked eye, making them the most effective filter type. The filter contains either fingers or grids (grid assembly shown) that is covered by a fine powder called diatomaceous earth. It is this powder that actually does the bulk of the filtering. DE powder is generally sold separately from the filter itself and is added by pouring it through the skimmer.
Like a sand filter, a DE filter must be backwashed when its pressure gauge reads 8-10 psi above its normal reading. Backwashing will flush most of the DE powder out of the filter. Your city may have certain DE disposal requirements, avoid backwashing into streams or sanitary sewer systems.
After backwashing, a new application of DE powder is added, via the pool skimmer. The grids or fingers in a DE filter should also be cleaned on an annual basis and soaked in a cleansing solution like our granular pool filter cleaner.
DE filters provide the highest water quality without a doubt, but this does come at a cost; the filters themselves are generally the most expensive and they are also more time consuming to maintain.
And the Best Pool Filter Type is…
- Sand filters are least effective but also the least expensive to buy and use.
- Cartridge filters are more effective but are more expensive to buy and use.
- DE filters are the most effective but are the most expensive to buy and use.
Determining the “best” filter for your pool will mean determining your feelings on water quality, price and maintenance. Your best pool filter may be the largest filter you can afford, no matter which filter type.
So remember – Go Big! A sand filter that is oversized for your pool is a better purchase than a DE filter that is undersized. Larger filters require less maintenance, the filter media lasts longer, and when you really need them – to clean up poor water conditions, larger pool filters will do so faster and better than smaller.
If you’d like us to help you select the filter that will give you the most filter size for your buck, give us a call at 1-800-288-7946!
InTheSwim Staff Blogger