At what pressure should you backwash a sand filter

Most guages very 32 pounds backwash some read some read up to 15 to backwash but the best way to know if it needs to be backwashed is put your hand in front of return outlet where your water enters pool, it should push your hand away quickly if not backwash

To all who have questions about the routine filter maintenance procedure (how's and why's), especially if it is a sand media filter.

• Sand does wear out, the scraggly edges of each grain where is the Way, with normal filter operation, and backwashing.
• Sand replacement should be approximately every 5 to 7 years. Each individual situation will vary
• Always use cleaned, pool filter sand. It is a #20 silica
• If a better media is needed, you can switch to crushed safety glass.
• There is no, one, magical number, of when to backwash your system. All systems will have a different number, as to when a backwash is required. Because of filter size, pump size, amount and length of plumbing, and the amount of fittings in that system. Is there a solar system, if so, that will increase the baseline starting pressure.
• When ever sand media is replaced, it is a good idea to make a notation of what that starting baseline pressure is, and use a sharpie marker, and write it, right on top of the filter tank.
• In my professional opinion, and experience that I have gained over the last 32 years in this industry, 6 to 8 is not exactly the correct number to monitor - the over back pressure, of the starting baseline pressure.
  • I would increase that range to a range of 6 to 10 pounds over the baseline starting pressure. Meaning, when the current monitored pressure is over the baseline pressure, by 6 to 10, it is time to backwashing that filter
  • It is common understanding, that the dirtier the filter, the more particulate it is able to filter out of the water.
  • 6 pounds over starting Baseline pressure, maybe just a tad too early to backwash? If the water is still flowing decent enough, and the water is still clear, try to get as close to the 10 pounds over baseline as possible.
  • But, again I will repeat... Every system will vary. I've got a procedure, that will work best for you.
• I recommend that at least once per season, if you're not monthly, use a sand filter cleaner, which uses an Enzymatic process to dissolve oil, and other organic contaminants.
  • It strips each individual grain of sand of what ever is creating a Goppy, gooey mess inside that tank.
  • Yes, those are technical terms, LOL.
  • Actually, that sludge is commonly created, in a heavily used pool, in a swim season. The dirt, body oils, suntan and other tanning lotions and oils, create a very sludgy, like molasses, substance in that tank. And this will not allow the water to filter through it. What also can occur, is little tunnels from the top of the sand bed, to the bottom manifold assembly, and this creates a direct access of water entering that tank, and flowing right to the manifold, as "unfiltered" water.
  • This is called channeling.
  • To alleviate this situation, it is recommended to use a sand filter cleaner.

If you go 28 psi or over on your gauge, you should then backwash. I typically backwash every couple of weeks to clean out my filter.

The back pressure at which it's time to backwash a sand filter is about 6-8 psi above the baseline pressure of a clean filter. Just after following the procedure to backwash and rinse your filter, check the sand filter's back pressure at the time you return the pump and filter system back into filter mode. This is the baseline pressure of your clean filter. As the filter gathers particulates from the pool water, the back pressure will rise over time, as indicated on your pressure gauge. Once the pressure reaches 6-8 psi above the baseline, it's time to backwash.

Some advice: Don't assume the baseline pressure will remain the same for your sand filter. The baseline pressure will change over time and when the sand media is replaced. Typicallly baseline pressure will go up slightly over a season due to captured particles that are difficult to backwash out. Use of a filter cleaner will help remove these captured particles.

More advice: Even with the use of filter cleaners and proper backwashing, sand media will not last forever. The constant water flow and movement of particles in the sand over time shears the surface of each little sand grain. Like a river flowing over rocks, over time each sand grain surface is smoothed, and thus its effectiveness for capturing small particles is reduced with ongoing use. A typical rule of thumb is to replace the sand media +/- 5 years. Some pool owners do it more often, some less. It depends on how long your pool season is each year and how much debris the filter much extract from the pool water.