How To Backwash A Pool Sand Filter

Sand filters are a great option for pool water purification as they typically have lower upfront costs and relatively easy to maintain.

This latest article, I’ll go through everything you need to know about backwashing your sand filter.

First, I’ll give a brief explanation of the purpose of a sand filter.

Then…I’ll dive into the simple steps to backwash your filter.

how to backwash a pool sand filter

What Does A Sand Filter Do For A Pool?

In a sand filter, pool water passes through the sand within which removes any dirt and/or debris. The purified water is then passed through the bottom and returned to the pool.

One of the few maintenance tasks you’ll need to perform on a periodic basis is to backwash it.

Under normal circumstances, your sand filter will have a multi-port valve system with 6 different positions.

These are:

  • Filter: Used for normal filtration or when you’re vacuuming the pool.
  • Backwash: Used to clean the filter sand. Pool water is reversed through the filter and passed through the sand then exits via the waste pipe.
  • Rinse: Used to clean water inside filter tank. This process should also be done every time filter sand is added or replaced.
  • Waste: Used for bypassing the filter tank and exit via a waste pipe (not returned to pool). Commonly used to lower the water level or drain the pool level to the bottom of the skimmer.
    Can also be used for vacuuming heavy concentrations of dirt directly to waste rather than being passed through the sand filter.
  • Closed: Use to completely shut off the flow to the filter and pool.
  • Winter: Used when closing a pool in areas especially where water can freeze.
  • Circulate: Use for bypassing the filter tank and return to pool.

What Is The Purpose Of Backwashing A Pool Filter?

Water from your pool is used to pass through the sand and instead of returning back to your pool, it is redirected out through a waste pipe.

This process removes any dirt, algae and visible contaminants / debris from your sand filter.

Doing so keeps your sand filter operating at optimum performance levels.

How Often Should You Backwash?

As sand filters are not as effective as cartridge filter in removing finer particles, it’s important to backwash on a frequent basis.

A good rule of thumb is to backwash once the pressure displayed on your pressure gauge is 8-10 psi over the starting level. Most pressure gauges on sand filters have a red and green zone.

When the needle is close to or within the red zone, it’s a good time to backwash.

Also, backwashing whilst killing an algae bloom or when trying to treat cloudy water will remove any algae deposits within the sand and keep your filter working effectively.

How To Backwash Your Pool Sand Filter


Turn off your pool pump. (Very important)


Set the sand filter multi port valve handle to the BACKWASH position and ensure the handle locks in place.


Turn on the pump and allow the sand filter to backwash for 2-3 minutes or until the water in the sight glass (typically located on the top of the filter) is visibly clear.

How long you backwash the sand filter for is not critical though you should visibly see clear water within 2-3 minutes.

Remember whilst your backwashing, you are losing pool water down the waste pipe (typically a drain).

It would be normal to lose up to 500 litres of water during this process.


Turn off your pool pump. (Very important).


Set the sand filter multi-port valve handle to the RINSE position and ensure the handle locks in place.


Turn on the pump and run the rinse process for 1-2 minute or again until the water in the sight glass is visibly clear.


Turn off your pool pump. (Very important).


Return the sand filter multi-port valve handle to Filter and ensure the handle locks into place.


Turn on the pump and continue to run under normal operating conditions.

Can You Backwash Too Much?

If you backwash your pool too much i.e. time duration and/or close frequency then yes you can cause a lot of problems.

Some problems that can arise from backwashing your sand pool filter too much are:

  • Loss of water – 500+ litres of water can be lost in each backwashing cycle
  • Loss of silica sand resulting in increased consumption and replacement costs
  • Dilution of chemicals resulting in higher sanitisation costs
  • Lower overall filtration quality and lifespan.

When Should You Change The Sand In Your Pool Filter?

Over time, the sand inside the filter loses its coarseness and becomes smooth and round. This makes it very hard for the sand to catch really small debris particles. Every 3 to 5 years you should change the sand in a pool filter.

Sand filters are perfect filters for almost any type of pool, although as previously mentioned they do require a bit of maintenance.

As you now know, backwashing is easy to do and should become part of your regular pool maintenance schedule.

Remember, for piece of mind always keep an eye on the pressure in your filter and if it gets too high, go ahead and backwash your sand filter.

A clean filter is key to a clean and healthy pool and will help you maintain the highest water quality possible so your family and friends can enjoy your pool during the summer.

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Using our computerised water testing equipment, we’ll give you a fast, accurate diagnosis about the condition of your pool water and prescribe exactly what your pool needs to keep it in great condition.

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