Your pool looks hazy and the water feels slow coming back into the pool. Most owners reach for more chlorine. The filter is usually the real problem.
Backwashing is how you flush the dirt out of a sand or DE filter. It takes about five minutes. The hard part is knowing when.
Read the gauge, not the calendar
Look at the pressure gauge on top of your filter. Write down the number you see right after the filter is cleaned. That is your clean pressure.
When the gauge climbs 8 to 10 PSI above that number, it is time. That is the whole rule.
A clean filter runs somewhere between 10 and 20 PSI on most home pools. If yours reads 28 and it was 18 when clean, you are due today.
Backwashing a cartridge filter is not a thing
Check your filter type first. A cartridge filter has no backwash valve at all. You open it and rinse the cartridge by hand.
Sand and DE filters are the ones with a valve. If you see a handle with settings printed around it, you have a multiport valve. If you see a lever that slides up and down, you have a push-pull valve.
Turn the pump off first
This is the step that breaks filters. Never move the valve while the pump is running.
The spider gasket inside a multiport valve is soft rubber. Water pressure shreds it when the handle turns under load. A new gasket is cheap. Getting to it is not.
So: pump off, then valve, then pump on. Every time.
The steps in order
Roll out your backwash hose and point it somewhere the water can drain. You are about to send a few hundred gallons out of the pool.
Turn the pump off. Set the valve to BACKWASH. Turn the pump on and let it run.
Now watch the sight glass, which is the little window on the valve. The water runs brown at first. When it runs clear, you are done. That usually takes two to three minutes.
Turn the pump off again. Set the valve to RINSE. Run it 30 seconds to settle the sand back down. Turn off, set to FILTER, turn on.
Check the gauge one more time. It should be back near your clean number.
Top the water back up
Backwashing drops the water level. Add water until it sits at the middle of the skimmer opening again.
Too low and the pump sucks air, which can burn up the seal.
Losing more water than one backwash explains? Our guide on telling evaporation from a leak walks through the bucket test.
More is not better
Here is what surprises people. A slightly dirty filter cleans better than a spotless one.
The trapped dirt acts like a finer screen. Backwash every week out of habit and you keep resetting the filter to its worst state. Follow the gauge instead.
DE filters are the exception in one way. After every backwash you have to add fresh DE powder through the skimmer, or the grids run bare and the powder cakes on wrong.
When the gauge will not come down
You backwashed and the pressure barely moved. Something else is going on.
- The sand is packed hard or past its life, which is usually five to seven years.
- Oils and sunscreen have gummed the sand, and only a chemical filter cleaner will cut that.
- A DE grid is torn and powder is blowing back into the pool.
- The valve is leaking water to waste even in FILTER position.
The opposite problem matters too. Pressure that drops on its own means flow is blocked before the filter, usually a clogged pump basket or a skimmer full of leaves.
Both of these show up on our list of pool repair warning signs.
Where it fits in your routine
Backwashing is one job on a longer list. Skim, brush, test, and vacuum still have to happen. Our breakdown of what a weekly pool service includes lays out the order we work in.
We have been doing this in Victoria since 1968, and every tech on our repair crew holds a Texas RAIL license.
Not sure what your gauge is telling you? Call us at (361) 575-5821 and read us the number.
Frequently Asked Questions
How often should I backwash my pool filter?
Go by the pressure gauge, not a schedule. Backwash when it reads 8 to 10 PSI above the pressure you saw when the filter was last cleaned. For many pools that lands somewhere between two weeks and a month.
How long do you run a backwash?
Two to three minutes for most home filters. Watch the sight glass on the valve and stop when the water runs clear. Then rinse for about 30 seconds.
Can you backwash a cartridge filter?
No. A cartridge filter has no backwash valve. You shut the pump off, open the tank, pull the cartridge, and hose it down.
Why is my filter pressure still high after backwashing?
The sand may be packed, worn out, or coated with body oils. Sand usually needs replacing every five to seven years. Oil buildup needs a chemical filter cleaner, not more backwashing.
Do I add DE powder after every backwash?
Yes. A DE filter loses its powder in the backwash. Add the amount your filter calls for through the skimmer with the pump running, or the grids run bare.
Does backwashing lower the water level?
It does. Expect to lose a few inches. Refill until the water sits at the middle of the skimmer opening so the pump does not pull air.
