Backwash Pool Sand Filter? Best Frequency Explained!

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How Often Should You Backwash Pool Sand Filter?

The pool sand filter keeps your water clear and safe by trapping dirt and debris as the pump pushes water through the sand. Over time, the sand becomes dirty and less effective, requiring backwashing. But how often should you backwash?

Backwash only when the pressure reading is about 10 psi higher than normal. Avoid frequent backwashing, as a bit of dirt in the sand can actually improve the filter’s effectiveness.

To begin with, the sand in your filter is totally clean. It is easy for the pump to push the water through it. You should make a note of the pressure reading at this point. This is the “normal pressure”. 

The normal pressure depends on the pool, pump and filter configuration. Generally, it will be between 5-25 psi.

With time, the dust particles start getting trapped by the sand. This makes the pores smaller. This is a good thing, initially. It allows the filter to trap even smaller solid particles.

However, the pump needs to work harder & harder. The pressure reading keeps rising. It is time to backwash the pool sand filter when the pressure reaches 10 psi above the normal pressure.

Pressure reading higher than this is not good for the pump and can even get risky. By backwashing you clear up the dirt from the sand pores making it easier for the water to flow through once again.

How Many Times a Month Should You Backwash a Pool?

The time to backwash your pool sand filter depends on the pressure reading. It is not necessary to backwash it at a fixed interval. Backwashing a pool sand filter, when it is not required, will waste pool water and expensive pool chemicals along with it.

Having said that, generally speaking you will need to backwash the pool sand filter once a month. 

You may need to backwash your pool sand filter more often depending on the weather condition too!

The amount of dirt and other contaminants in the pool can go up during:

1. Summer: 

The pool gets used more during the peak summer months. Kids have summer breaks, the days are longer and it is hot! The coolest place to be in, without doubt, is the swimming pool. Expect and plan to backwash more often!

2. After Storms:

Rain & Dust storms will dump a lot of dirt, dust & yard debris into the pool. The risk of “algae bloom” also goes up. You will need to shock your pool more often. The filter will also be overloaded with dirt. So, be prepared to backwash more frequently!

3. Fall:

You & your family will not be using the pool too much during fall. But now you have dry leaves being blown into your pool. They can be, and should be skimmed out as often as possible. Nonetheless the frequency of backwashing may need to go up!

How Long Should You Backwash Your Pool?

To backwash a pool sand filter, turn off the pool pump first. Position the valve handle to BACKWASH and turn on the pump.

Just a few (2-4) minutes of backwashing is enough. Keep an eye on the sight glass. When the water is running clear, you can stop backwashing.

Now turn off the Pump, position the valve handle to RINSE. Turn on the pump and rinse for 30-60 seconds. Rinsing is the process where the water runs in the correct direction, but to waste. This is when the dirty water is expelled from the pool system. 

You can now run the pool sand filter on the FILTER position.

For more detailed information on all settings check out my post Pool Multiport Valve Settings (The Best Guide With Simple Schematics!).

Can You Backwash Your Pool Too Much?

Actually, you can if you follow a fixed time schedule, instead of backwashing based on the pressure reading.

It is, of course, extremely important to backwash the pool sand filter when the pressure gauge is 10 psi above normal reading. But if you backwash much earlier than that, you will lose some pool water. 

Expensive pool chemicals go out along with it and you will need to add them back to get the pool water chemistry in line.

You also lose the initial dirt trapped in the filter medium. The initial dirt build up constricts the pores in the sand and helps in trapping even smaller solid particles.

Recommended Pool Sand Filters

Best Sand Filter

The Hayward Pro Series Sand Filter for in-ground swimming pools will provide you with hassle-free, effective filtration. The weather-proof tank is constructed of a tough, color-fast polymeric material.

Even water distribution over every square inch of sand is ensured by an integral top diffuser, self-cleaning under drain and 360 degree slotted laterals. Advanced full-flow technology reduces energy costs by achieving excellent filtration, so you can run your filter less.

Thorough backwashing allows for crystal-clear water. Filter is complete with tank, 7-way multi-port valve, sight glass and pressure gauge. 7-way Valve Positions: Filter, Waste, Winter, Closed, Backwash, Recirculation, Rinse.

Hayward Pro Series Pool Sand Filter

Thank you very much for reading the post. I do hope you found it informative and helpful.