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How to Select the Best Pool Filter

Barack has expertise in pool chemistry and pool maintenance. He writes in-depth articles about how to maintain pools for optimal enjoyment.

The right pool filter depends on the pool size, usage and where it is located.

The right pool filter depends on the pool size, usage and where it is located.

How Pool Filters Compare

A well-serviced swimming pool starts with the filter: most swimming pools will turn cloudy or keep pool algae due to a poor filtration system. Filters come in different brands, types, and sizes, but there is no single filter that is the best. Rather, the best choice depends on your pool size, where it is located, and how often you use it.

Three Types of Pool Filters

  • Sand filter
  • Diatomaceous earth (DE) filter
  • Cartridge filter

This article includes a comparison of all three, looks at the pros and cons of each, discusses which one to use where, and then details how to maintain and troubleshoot problems.

Who Should Get a Sand Filter?

  • The sand filter is the most common type of pool filter. It uses grains of sand to trap debris as the pool water passes through it.
  • In terms of efficiency, it removes debris in the pool water down to about 40 microns in size, which is adequate for most situations.
  • It is always the best option for highly trafficked pools like the ones in hotels, apartments, public clubs, and so on. This is because it does not clog easily like the DE and cartridge filters, which will need lots of maintenance and replacement of filtering medium after a short period of time.

Sand Filter Maintenance

The sand filter is probably the easiest to maintain. Whether above-ground or in-ground, pool maintenance mainly involves backwashing and changing the sand grains.

For a well-serviced swimming pool, backwashing a sand filter should be done whenever the pool pressure rises to five to eight pounds above the normal pressure. This might happen every two days in a busy swimming pool. For a home pool that is not very busy, this can be done after every one week.

How to Backwash a Sand Filter

  1. Empty the skimmers so that trapped leaves and debris do not get back into the pool after backwashing is finished.
  2. Turn off the pump and empty the pump trap basket.
  3. Ensure that the cutoff valve in the filter is opened prior to backwashing, if the filter has one, to prevent it from blowing up when pressure accumulates.
  4. Put the backwash valve on "backwash" and turn the pump on; let it run until the water in the sight glass turns clear.
  5. After the water in the sight glass turns clear, turn the pump off and switch the backwash valve to "rinse" and let it run until the sight glass runs clear. Alternatively, If the filter has a plunger valve, skip to step 6.
  6. Turn the pump off and put the backwash valve in the filter position.
  7. Turn the filter back on.

Replacing the Sand in Your Filter

Sand grains used in filtering have sharp edges that help in trapping debris as water passes through the filter. The sharp edges wear with time and sand grains become ineffective in filtering the debris as needed. Because of this, sand should be replaced at least after every five years for a home swimming pool, and after two to three years for public or semi-public swimming pools.

However, sometimes a sand filter may fail to filter effectively before two years elapse, depending on how busy the pool is. Some swimming pool managers use an additional filtering medium such as ZeoBrite, Pebble, and Pea gravel with the old sand to improve its effectiveness in trapping debris.

How to Change the Sand in Your Filter

  1. Backwash the filter and put off the pump.
  2. Remove the filter lid and remove all the sand.
  3. Ensure the air relief tube is connected to the bottom pipe.
  4. Fill the filter halfway with water and add the correct amount of new sand, preferably 20 grade silica sand.
  5. Start the backwash on the filter and backwash until the sight glass runs clear.
  6. Turn the pump off, put the filter back on the filter, and turn the pump on.

Troubleshooting: Signs That Your Sand Filter Is Faulty

Detecting a problem with your sand filter may be time-consuming. If the sand in your filter goes bad, you cannot tell just by looking at it.

However, there are a couple of signs that show that the sand in your filter is not effective and should be changed.

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Read More From Dengarden

Cloudy Pool Water

Water clarity may be affected by a number of factors including pool chemistry and pool filter.

If your pool is cloudy and you are sure it is not caused by water chemistry, then most probably it is the sand in your pool filter. The next thing will be to replace the sand in your pool filter.

Short Backwash Cycles

Short backwash cycles happen if you find yourself backwashing your filter more than once per day. If this is the case, the sand in your filter is clogged or it is undersized. If clogged, the only solution for your filter is to replace the sand.

Sand Returning to the Pool

If you find that lots of sand returns to the swimming pool, the only problem would be with your filter laterals. You will need to remove the sand in your filter and ensure that any breakage is corrected.

Moreover, sand may return to the pool especially after a backwash due to displaced or missing air relief tube in the filter.

If this is the case, the filter will have to be opened to make sure that the air relief tube is secured in its place firmly.

Who Should Get a Diatomaceous Earth Filter?

A DE filter offers the best possible filtration when it comes to effectiveness, but it also requires the highest level of maintenance compared to the sand filter.

A DE filter removes debris down to about five to eight microns. It is the most preferred filter to use in pool water with metal compounds such as iron and copper.

However, it is not the best option for heavily used pools, such as commercial swimming pools, due to ease of clogging and high levels of maintenance.

DE Filter Maintenance

A DE filter should also be backwashed when the pressure goes to 5–8 pounds above the normal pressure; or after every four weeks.

If the backwashing cycle goes below three or four weeks for home pools, then it is time you arrange for your DE filter cleaning. This cleaning should be done at least once or twice every year.

How to Backwash a DE Filter

  1. Empty the skimmers.
  2. Turn off the pump and empty the pump trap basket.
  3. Ensure that the cutoff valve in the filter is opened prior to backwashing if the filter has one, to avoid blowing up when pressure accumulates.
  4. Put the backwash valve on "backwash" and turn the pump on, let it run until the water in the sight glass turns clear.
  5. After the water in the sight glass turns clear, turn the pump off and put the backwash valve in the filter and let it run for about 10 seconds. If you are using a multiport valve instead, use the "rinse" setting.
  6. For better results, repeat steps 4 and 5 three more times.
  7. Turn the pump off and put the backwash valve in the filter position, and turn the pump back on.
  8. Add the right amount of DE filter reagent through the skimmer.

How to Clean a DE Filter

If your filter backwashing has a short cycle, basically less than three or four weeks, then you need to clean your DE filter.

Most DE filter manufacturers will recommend cleaning filters one or two times every year. Here are the steps involved when cleaning a DE filter.

  1. Backwash the filter.
  2. Allow the air to be drawn into the tank by opening the air relief valve, this will break the vacuum inside the tank.
  3. Separate the two halves of the filter.
  4. Remove the filter grid assembly and disassemble it if it comes out intact.
  5. Spray each piece with a garden hose pipe to remove all the dirt and debris. You may need a filter cleaner if some dirt or oil is stuck after using a hose pipe.
  6. Loosen the bulkhead fittings and physically remove the tank and clean it out of the tank.
  7. Reassemble the grid assembly and tighten the connecting rod firmly in place.
  8. Put the grid assembly back in the filter.
  9. Put the top half of the filter back on and restart the pump.

Troubleshooting: Signs That Your DE Filter Is Faulty

A DE filter is pretty easy to troubleshoot than a sand filter. Moreover, the filter medium in DE filter does not go bad since it is changed every time backwash is done.

Basically, the filter elements or parts will go bad. However, troubleshooting a DE filter is straightforward, and there are signs you can look for to detect spoilt parts:

DE Filter Powder Returning to the Pool

If the DE filter parts are damaged, the DE will definitely go back into the pool. If this is the case, then the problem with your DE filter may be in one of the following parts of the filter:

  • Torn Filter Grids: A hole may develop anywhere on the fabric of the grid. Ensure that you look carefully to find if there is a hole in the grid and fix it.
  • Broken Manifold: If the manifold is broken, a large amount of DE will return to the pool.
  • Broken or Missing Air Relief Strainer: A broken or missing air relief strainer will allow the DE into the pool water.
  • Bad Backwash Valve: The problem may be with the backwash valve, disassemble the valve and inspect it for any damage that may be allowing DE back into the pool.
  • Broken Filter Necks: Check and ensure that your filter neck is intact, loose or broken filter necks cause DE to go back into the pool.

Who Should Get a Cartridge Filter?

The cartridge filter is the cheapest filter around and the easiest to maintain since it uses a filter medium that is easy to clean and replace.

Cartridge filter should be cleaned when the pressure goes to five to eight pounds above normal, like all the other filters.

Large capacity filters of 300 square feet and above may require being cleaned on an annual or semi-annual basis.

Cartridge Filter Cleaning Process

  1. Disassemble the filter.
  2. Remove the cartridges and clean them using a normal garden hose pipe.
  3. If some dirt or oil are stuck and not removed with the hose nozzle, you may need a special cleaner, if that fails too; it is time to replace your cartridges.

Troubleshooting: Signs That Your Cartridge Filter Is Faulty

Cartridge filters will allow debris to return to the pool if they become ineffective. It may be very difficult to detect the exact location in the cartridge that is causing the filter problem.

However, the main sign that your cartridge has a problem is when debris returns into the pool.

Other parts of the cartridge filter that may cause a problem with the filtration system are torn filter material, missing fittings, and a broken or missing air relief strainer.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: How do you lower high stabilizer level?

Answer: The only way to lower Cyanuric Acid in your swimming pool is to drain your pool water and then fill the pool with fresh water. You should be doing the process as you take the reading if Cyanuric Acid until it is stable around 50 ppm.

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