How Long Should You Backwash Your Sand Filter?

Dirt and debris build-up in your sand filter makes the filtration process less efficient, leaving your pool water looking cloudy and gross. Backwashing your sand filter restores its cleaning ability so you can get back to swimming in clear and clean water. So, how long should you backwash your sand filter?

You should backwash your pool sand filter for about 2-3 minutes or until the water in the sight glass or drain outlet becomes clear. Remember to rinse the filter after backwashing to prevent any remaining junk washed from the sand from getting pumped directly into your pool.

Let’s look at how backwashing works, how often you need to do it, and what may happen if you do it for too long.

What is Backwashing and How Does it Work?

Pool cleaning with a pump

Backwashing a filter like this one (on Amazon) is a method of thoroughly cleaning a swimming pool’s filter to remove the accumulated contaminants without having to do it manually.

As pool water passes through the filter, it traps dirt and debris, which build up in the filter medium. Eventually, the filter medium becomes clogged, reducing your filter’s performance. 

Backwashing swoops in and saves the day as it sends water back through the filter, which lifts and flushes the filter media and then gets rid of the dirty water via a waste or drain port. This forces out all the dirt and debris stuck in the filter and restores it to its average functioning level.

How to Backwash a Sand Filter

Backwashing is an essential procedure that you need to perform regularly. Here’s how to backwash a sand filter:

  1. First, turn off the pool pump.
  1. Set the sand filter multiport valve handle to Backwash and ensure it locks into place.
  1. Turn the pump back on and backwash for 2-3 minutes or until you notice the water in the sight glass is clear.
  1. Turn off the pump again.
  1. Set the filter valve handle to Rinse and ensure it locks into place.
  1. Turn on the pump and rinse for around 1-2 minutes or until the water in the sight glass is visibly clear.
  1. Turn off the pump.
  1. Return the filter valve handle to Filter and ensure it locks into place.
  1. Turn the pump back on and continue to run it as you usually do.

How Long Should You Backwash a Sand Filter?

You should backwash your sand filter for around 2-3 minutes or until the water in the sight glass on top of the filter becomes clear. While backwashing, you’re losing pool water down the waste pipe, so don’t do it for too long.

How Often Do You Need to Backwash a Sand Filter?

As a rule of thumb, you should backwash your sand filter weekly. But if you’ve used your pool more than you usually do, you can backwash it twice a week. The best time is right after vacuuming your pool. 

You should also backwash your filter if the pressure gauge shows 5-10 psi higher than the normal operating pressure—between 10-25 psi.

When the filter gets dirty and clogged up, the pressure reading skyrockets. Additionally, if your pool is prone to leaves or other tree debris, you may need to backwash it more frequently.

What Happens if You Backwash for Too Long?

Backwashing your sand pool filter for too long is a recipe for disaster. It can cause a lot of problems to your pool, including:

  • Loss of silica sand leads to increased replacement costs.
  • Loss of up to 500 liters of water during each backwashing cycle.
  • Dilution of chemicals results in increased sanitization costs.
  • Reduced overall filtration quality and lifespan.

Can You Backwash a Cartridge Filter? 

Replacement of water filter valve

Because cartridge filters aren’t designed for reverse water flow (you can’t backwash them simply by reversing the flow of water in the pool’s filter system), you must clean them by hand whenever they get too filthy.

An excellent, thorough cleaning with the garden hose is often enough, but you’ll need to clean it using chemicals if you have to clean your filter every three or four days. Here’s a basic guide on cleaning a cartridge filter:

Step 1: Turn off the Filter and Shut the Valves

Switch off the filter, close the valve from the filter outlet leading to the pool inlet and close the valve that goes from the skimmer to the pump inlet. 

If you have no valves at these connections, insert a plug into the skimmer to cut water flow into the pump and another plug at the pool inlet to prevent the backflow of water into the filter housing.

Step 2: Loosen the Air Valve

Loosen the air valve to slowly release pressure and allow air into the cartridge filter housing.

Step 3: Open the Filter Drainage Valve

Find the filter drainage valve at the base of the filter housing and open it. This will empty the trapped water in the filter housing so it won’t recontaminate your clean filter when you reinstall it later.

Step 4: Access the Cartridge

Take the top off the filter housing to access the cartridge. Depending on your cartridge filter, you may have to unlock a safety latch. Go through the manufacturer’s instruction manual to find out how to unlatch and remove the top.

Step 5: Hose Down the Filter

Set your garden hose to the most powerful setting and hose off the cartridge filter to remove any debris stuck in it. Be sure to hose off inside the filter housing as well.

Step 6: Prepare a Cleaning Solution

Prepare a chemical cleaning solution for your filter in a large container that can fit the entire filter. Mix one cup of trisodium phosphate (TSP) with four cups of water, repeating this ratio until your filter is fully submerged in the solution.

Step 7: Let the Cartridge Soak

Soak the pool cartridge overnight in the TSP solution, then rinse it off with your garden hose.

Step 8: Place the Top Back On the Filter Housing

Return the top on the filter housing. Also, make sure that the O-ring on the filter housing is seated correctly and the housing is secured. Replace the O-ring if it’s flat, cracked, or decaying.

Step 9: Close the Drainage Valve 

Close the drainage valve and open the filter and pump inlet valves. Unplug the skimmer and pool return inlets if you plugged them earlier.

Step 10: Turn on the Filter

Switch on the filter and open the air relief valve at the top of the filter. When the water starts spraying out, close the air valve. That’s it! Your cartridge filter is now ready to continue cleaning your pool water.

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