How Often Should a Swimming Pool be Backwashed?

Your pool maintenance routine can get quite complicated, and backwashing is one of those tricky tasks. One of the most prominent questions I get is how often a pool should be backwashed.

You should backwash and rinse your filter about once a week. You will want to backwash the filter immediately after vacuuming your pool. You might also want to backwash your pool if the suction seems to be dropping or your pump is straining, this means that the filter might be clogged up with dirt.

Water filtration in your pool is extremely important for the health of the pool as well as that of the swimmers. All kinds of germs, viruses, and bacteria can thrive in pool water.

Keeping your filter backwashed and clean also increases the longevity and efficiency of the pool pump and the filter. Read on for more tips on backwashing and general maintenance.

Some Backwashing Scenarios

Once a week.
It is a good idea to work this task into your weekly maintenance schedule. Backwashing once a week is usually enough to keep your sand filter clean and your system running efficiently.

Immediately after vacuuming your pool.
In addition to your weekly backwash, you will need to backwash your pool immediately after vacuuming your pool. All that algae and debris you’re sucking up is going to clog your filter up, which leads me to my next point…

When suction is decreasing and your pump is straining.
When your filter is dirty, the pressure increases as the water tries to push through the clogged up sand. This will cause your pool pump to strain and you will easily be able to hear this in the high pitched hum your pump will make. When this happens, it is time for a good old backwash.

What is the purpose of backwashing a pool filter?

Essentially, what you are doing is cleaning the filter.

But to answer that in more detail lets first try to understand how the pool filter works. We’ll start with the normal cycle of the pool water through the filter, and then talk about the cycle during the backwash.

The normal cycle of the pool water.
When your filter runs normally, the water is pumped from your pool, through the filter and back into the pool. After a while, debris, dirt, and oil saturate the filter sand and can eventually “clog” up the filter and some dirt might even make its way back into the pool. The clogging of the filter will also cause a noticeable pressure rise in the filter and will put additional strain on the pump.

The cycle of the pool water on backwash.
When you set the valve to backwash, the flow through the filter is reversed and the water is pumped from the pool, through the filter, and out as wastewater. Because the water flows through the sand filter in reverse, it lifts the sand and washes it free of dirt, which is then expelled out of the system through the waste pipe.

You will notice that in the first minute or so the water will be dark and murky, you must continue the backwash until this water becomes clear.

What happens when you don’t backwash your pool filter?

When you don’t backwash your pool filter for an extended period of time, you will find that as the sand inside the filter gets dirtier and more clogged up, the pressure in the system from the pump to the filter will increase, and the suction will drastically decrease.

This increased load on your pump can eventually damage your pool pump. The reduced suction will also render your automatic pool cleaner/vacuum useless.

Can I backwash my pool too often?

Yes, you can. Each time you backwash your pool, very little amounts of sand will be washed out. Over time, this might add up and your sand level will lower to a point where your filter is not cleaning efficiently anymore.

Backwashing too often can produce less efficient filtration, you don’t want your sand to be too clean. Little particles of dirt trapped between the sand actually help to filter the water better. Some say that half dirty sand performs twice as well as fully clean sand.

Keep in mind that you are also wasting a lot of water during the backwash. So figure out what is the best backwashing schedule for your pool and stick to that.

Why do I constantly need to backwash my pool filter?

You are not backwashing for long enough.
Make sure that you are backwashing the filter until the water coming out of the waste pipe is clear. This is when you have washed out the majority of the dirt from the filter. You may want to continue the backwash for another minute or two to be extra thorough.

The sand in your filter is mud-balling.
The oil that is caught in the filter might be causing the sand to form into solid clumps, making it difficult for the water to push through them, increasing the pressure in your filter and the load on your pool pump. Unfortunately, this means you may have to change out the sand in your filter.

The sand in your filter may be calcifying.
If you have left the sand in your filter for too long, it will start to harden and form rock-like formations inside your filter. Be careful as these calcifications may get past a point where you will not be able to remove them without damaging the piping inside your filter. Changing your sand every 3 years or so will help to avoid this problem.

Pro-TIP! Deep clean your filter. If you are constantly struggling, you can backwash your filter up to three times in succession for a good and thorough deep clean! Backwash the filter for 2 to 3 minutes, then run the system on filtration for 15 seconds. Now backwash for another 2 to 3 minutes. Repeat this 3 times

How do I change the sand in my pool filter?

If you find that your pool is always cloudy despite you having backwashed constantly, your sand in the filter might be so degraded that it is not cleaning the pool water efficiently anymore. You might also find that the sand level in your pool filter has lowered significantly. In either case, you will need to replace your sand.

This task is quite detailed, so instead of explaining it here in words, I found this very well put together video on YouTube.


Backwashing your filter sounds complicated, but it is simply a mechanism in the system to clean the sand in your filter. Nothing more.

Over time, dirt, grime, oil, and debris can clog up your sand filter. You need to clean this out by means of a backwash.

How often should a swimming pool be backwashed? You should backwash your pool every week. In addition to that, you should backwash it immediately after vacuuming.

Signs that your pool pump needs to be backwashed include, loss of suction, increased pressure in the filter, and increased strain on the pool pump. You’ll be able to hear it straining.

If you find that you have to keep backwashing your filter, you might want to try a deep clean by running the backwash back to back three times with 15 seconds on normal filtration in between each backwash.

Try not to backwash too often as this can increase the loss of sand and also wastes a lot of water.

If your filter is not cleaning efficiently and your pool is constantly murky, your sand is probably worn out or mud-balling and needs to be replaced.

PS. I got caught peeing in the pool today. The lifeguard blew his whistle so loud I almost fell in…

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