How to Backwash a Pool Filter

Written by Michael Dean
June 16, 2023

pool filter next to a swimming pool

Backwashing your pool filter is the process of thoroughly cleaning the filter and the material inside it. The purpose of a pool filter is to trap debris and prevent them from re-entering your pool. When you backwash your filter, you flush those contaminants out and improve the efficiency and lifespan of your filter.

In this article, I will go over everything you need to know about backwashing your pool filter, including the why, the when, and the how, with my handy step-by-step guide. Everything should take less than an hour.

Main Takeaways

  • You should backwash your filter to relieve too-high water pressure, to better water flow, and to improve water clarity.
  • Backwash your sand filter every 2-4 weeks and your DE filter every 4-6 weeks.
  • When choosing between a sand or DE filter, consider your budget, how much time you have for maintenance, and the cleaning power.

Why You Should Backwash Your Pool Filter

Backwashing your pool filter is an easy and inexpensive way to extend the cleaning use of the sand or diatomaceous earth that filters your pool water. After a while, your filtering material will become backed up with the debris collected from your pool and will not work as well to keep your swimming pool clean.

While it is standard to backwash your pool filter every few weeks, depending on which filtering material you use, your pool will also give you signs that it is time to backwash your filter.

Water Pressure

The water pressure in your pool filter will increase when the system is straining to work efficiently or becomes clogged. Most pool filters should be around a ten-pound force per square inch (psi) and can operate between five and fifteen psi or between ten and twenty psi, depending on the system.

Water Flow

Too much dirt and debris will slow the flow of water passing through your filter, slowing the flow of water entering your pool. You can feel the difference in circulation from the water jets that push the water back into your pool.

Water Clarity

If your pool looks cloudy, it could be because of a backed-up filter. Backwashing your filter can help keep your pool water crystal clear. While cloudy water may also be attributed to chemical imbalances, backwashing your filter is a quick and less costly way to clear your water up.

When to Backwash Your Pool Filter

Typically, you should backwash sand filters every two to four weeks, and DE filters require backwashing every four to six weeks. If you lose track, you can also check your filter’s pressure gauge or your pool’s water quality.

Backwashing your filter after a heavy rainstorm will help to remove large objects that can get trapped in your filter during a storm. You should also backwash your filter when treating your pool for algae or trying to get rid of cloudy water.

Sand vs. DE Filters

When choosing between a sand or a DE filter, you should consider your budget, the time you have to put into maintenance, and the cleaning power you will need depending on usage and location.

Sand Filters

Water flows into a pool sand filter tank and is pushed down through the sand. As the water moves through the sand, the filter purifies it before releasing it back into the pool. Sand filters excel at catching large dirt and debris, but may not capture all of the smaller particles that pass through the filter.

Sand filters were the first to filter pool water and are still the most commonly used today. DIY pool maintenance is straightforward with a sand filter, and pool-grade sand is inexpensive to purchase and replace.

There are three main types of pool sand. It is essential to always use pool-grade sand if you choose to run a sand filter:

  • Silica is naturally mined quartz ground into fine sand that can easily trap particles in your pool water. It is inexpensive, making it the most popular option for pool filter sand today.
  • Glass sand is made from recycled glass material. It is an environmentally-friendly way to maintain your pool. Glass has a negative charge, allowing it to capture manganese and iron particles efficiently, so glass pool sand is best for pools filled with hard water.
  • Zeolite sand is created from minerals found in volcanic rock. Its unique honeycomb shape helps zeolite sand easily capture dirt and debris from your pool.

If you’re running a sand filter, read my guide on replacing filter sand and how to get rid of sand that leaks into your pool.

DE Filters

DE, or diatomaceous earth, filters use the fossilized remains of microscopic diatoms. These diatoms are algae-like organisms that form sedimentary rock. The sedimentary rock cleans the water as it runs through a DE filter.

If you want the cleanest pool possible, consider a DE filter. DE pool filters can filter out the smallest particles from your pool water, keeping your water crystal clear. However, they also require the most upkeep and are more costly to maintain. You will need to add more diatomaceous earth powder after backwashing your DE filter and ensure that it coats the sides of the filter.

How to Backwash a Sand Filter

Backwashing a sand filter is easy to do on your own by following these easy steps.

1. Turn Off the Pump

Completely turning off the pump will prevent any new water from entering the filter while you are working on it.

2. Switch the Setting on the Valve

Once the pump is off, you can change the setting on the pool filter valve to “backwash.”

3. Attach the Backwash Hose

Position your hose over the backwash nozzle and secure it with a metal hose clamp. You may need a screwdriver to ensure the clamp is tightly secured.

Then, position the backwash hose where you would like the water to discharge. If you don’t have a backwash hose, check out my article on the best pool backwash hoses.

4. Turn the Pump Back On

Run your pump on the backwash setting for two minutes. While waiting two minutes on the backwash setting is standard, you can also determine if your filter is clean by watching the sight glass. Once the water flowing through the sight glass is clear, you will know your filter is clean.

5. Turn Off the Pump

Once the backwash cycle is complete, turn the pump switch off again.

6. Switch the Setting on the Valve

Once the pump is entirely off, change it to the “rinse” setting, and rinse for one to two minutes. The rinse setting will flush out any dirty water that remains in the filter.

7. Return the Filter to the “Filter” Setting

After the filter has rinsed out, turn the pump off and return to the original filter setting. Once the filter has run for an hour or so, check the gauges to ensure nothing is leaking. If there are no problems, you can run the filter as you normally would until it is time to backwash again or change your filter sand.

Below is a YouTube video that explains all the steps I covered, just in case you’re a more visual learner.

How to Backwash a DE Filter

Backwashing a DE filter is different from backwashing a sand filter, but easy to do on your own.

1. Turn Off the Pump

Switch off the pump motor before you start backwashing to prevent new pool water from entering the tank.

2. Switch Valve to “Backwash” Setting

Push down on the multiport valve handle and rotate it from “filter” to “backwash.”

3. Prepare for Backwash

Attach a waste hose to your filter.

4. Turn On the Pump for Backwash

Be sure you open the air bleeder assembly on the filter and watch for backpressure or hose kinks. If the pressure builds, you must turn the pump off immediately.

If everything is running smoothly, run the backwash setting for two to three minutes or until the water becomes clear.

5. Switch Valve to “Rinse” Setting

Turn the pump motor off before moving the valve setting to rinse. Run the filter on the rinse setting for up to ten seconds before turning it off and switching back to the backwash setting. Continue alternating between backwash and rinse at least three more times.

6. Return Valve to “Filter” Setting

Shut everything off before returning to this setting.

7. Add More DE Powder

Add one pound of diatomaceous earth powder for every 10 square feet of filter area. Your filter tank should also tell you how much powder to add. I recommend using one-half cup less than what you are supposed to add because powder is always left. Too much extra powder could clog up your filter or cause other problems.

Here’s a good replacement DE powder if you don’t already have some.

Robelle D.E. Powder for Swimming Pools

Robelle makes a good replacement DE powder you can use when you're backwashing and cleaning your DE filter.

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I may earn a commission if you make a purchase, at zero additional cost to you. This in no way impacts my research process or opinions.

And here’s a video covering these DE filter backwashing steps, in case you want to follow along visually.

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The Bottom Line

Whether you choose to clean your pool with a sand or DE filter, you can easily backwash it on your own. All pool filters follow the same general steps for backwashing, but there may be slight variations depending on the model you own. The owner’s manual should have detailed instructions for backwashing your filter.

If you’re hesitating between a sand and DE pool filter, the backwashing process is one of the things to consider to make the best decision possible. DE filters tend to cost more, but you don’t need to backwash them as frequently as sand filters. If you want to reduce pool maintenance as much as possible, a sand filter would be a better option for you. You can check out my specific model recommendations in my research on the best pool filters for inground pools.

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