Swimming Pool Filter Buying Guide - Sand Filters

Posted by Sean McKenna on

If you have a rough concept of how the human body operates you are likely aware that the heart is the ‘pump’ that drives blood, via arteries, to the rest of the body. To expand the analogy a little further you may be aware that the function of our kidneys is to clean our blood by filtering the waste. In a pool circulation system the media filter plays the same pivotal role as the kidneys in our body. As water passes through the filter small micro-organisms are captured within the media so that the cleansed water can return back to the pool.

There are typically three styles of filter available for a swimming pool with each having their own benefits and drawbacks dependent on the unique parameters of the pool. The three types of filter are sand, cartridge, and diatomaceous earth which is often referred to simply as D.E.

Sand Filters

How do they work?

Sand filters are large tank bodies with a multi-port valve located on the top or to the side of the tank. The filtering medium, as you would guess, is *typically a bed of coarse silica sand. Silica sand should not be confused or replaced with playground or mortar sands. Silica sand has jagged edges to help trap particulate matter as it passes through the tank body.

How well does a sand filter perform?

The filtering capacity or efficiency of a filter is measured in ‘microns’. A sand filter can remove debris as small as 25 microns. A micron is a measurement which is represented as one millionth of a meter. For reference; table salt is 100 microns, human hair is 70 microns and the limit of human visibility is 40 microns. So if someone says they have a certain type of filter because they can see the difference....refer them back to this blog.

How do I know what size of sand filter I need?

First rule of sand filter sizing is get the biggest filter that you can physically fit in the existing space. This will ensure it can handle the incoming flow from pump but also means that it will require less frequent backwashing.

The effective filtering rate of a sand filter is determined by the surface area of the sand bed. The tank bodies range from 16” to 30” in diameter for residential applications which equates to about 2'-5' ft2 of filtering capacity. A sand filter can effectively process 5-20 gpm/ft2 which means a 24" filter, with a surface area of 3.19' ft2 can support a pump that pushes up to 65 gpm.

How much do they cost?

Residential sand filters are the most cost-effective means of filtering water. They range in price from $400 - $1500 dependent on the size required.

How much maintenance is involved in a sand filter?

From a maintenance perspective they are also the least amount of regular routine. When a sand filter is burdened with debris (leaves, silt and other organics) and requires cleaning it is as simple as rotating the valve on the filter to 'backwash' and allowing the filter to clean itself with pressurized water from the pump. You may have heard someone say that sand filters require a regular backwashing routine ie. once per week. This is not true. A sand filter should not be backwashed/cleaned until the pressure, as outlined on the pressure gauge included with the filter, has increased about 7 lbs. This may take weeks depending on the unique parameters of the pool. A sand filter will operate more effectively as debris accumulates until a backwash is needed. Conversely, cleaning the filter too often lessens performance.

Over time sand media may require cleaning in order to remove any oils that have built up on the individual granules. This can be done by adding a demulsifying chemical for swimming pool filters.

In time the sand media of a sand filter does need replacing. Some industry members make a routine of changing sand every 5 seasons however I have experience with pools with 15 year old sand beds that still perform as new. The sand should not be replaced unless it no longer offers effective filtration. Before replacing the sand it should be cleaned and confirmed that there is not an issue with the filter internals or related parts.

What type of pool makes a great fit for a sand filter?

  • a pool that has a fair amount of debris (leaves, pine needles, sand/silt)
  • a pool that uses a suction side cleaner to vacuum the debris
  • a pool that is subject to frequent (yet preventable!) algae blooms
  • a pool that is winterized with a mesh safety cover will be easier to return to normal operation
  • any pool which would like to reduce maintenance
  • any pool which would like to reduce costs

 *alternatives to sand include glass media and Zeolite. Glass media (5 microns) and Zeolite (3 microns) both offer improved filtering capacity compared to sand but initial cost of the media itself is around 4x-5x more.

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