How to Backwash a Pool

Backwashing a pool reverses water flow through a sand filter or glass media to flush dirt and other contaminants to the waste line, then a short Rinse resettles the bed before returning the filter valve to Filter. Its important to note that you do not backwash cartridge filters. Clean those elements manually.

What does backwashing a pool filter actually do

Backwashing a pool sends pool water backward through the media so the bed loosens, backwash lifts the dirt, and the slurry exits via the backwash line or backwash hose. That backwashing process restores flow for optimum filtration, drops the pressure gauge toward your clean baseline, and helps prevent cloudy water. If you are weighing media types, compare here: Pool Sand or Cartridge Filter: Which is Better?.

How often should you backwash a pool

Use your own clean baseline. Backwash at a 20 to 25 percent rise in the pressure reading. Expect more frequent cycles after storms, heavy swims or algae cleanups. Pair pressure checks with weekly testing: Testing Pool Water.

Do all pool filters need backwashing

• Sand or glass media: backwash then Rinse.
• Cartridge filters: do not backwash. Remove and clean elements using Guide for Cleaning Pool Filter Cartridges.
• DE filter: backwash, then add the correct DE charge through the skimmer.

What PSI increase means it is time

Work from your system’s original position reading after a full clean. Backwash at +20 to +25 percent on the pressure gauge. Log results with a reliable kit from Pool Equipment: Pool Test Kits.

How long to backwash

Run Backwash for 1 to 3 minutes until the sight glass runs clear, then run Rinse for 20 to 30 seconds so the rinse process settles the bed and prevents dust from blowing back into the pool. Plan maintenance with your run windows: How Long Should a Pool Pump Run?.

Backwash, Rinse and Waste on the multiport

• Backwash: reverse flush to the waste port.
• Rinse: clears lines and rinse resets the bed.
• Waste: bypasses the filter system to drain. Handy when you vacuum heavy silt straight out. See How to Vacuum Your Pool Effortlessly.

Pump speed and valve handling

Use enough RPM for a strong, steady flush. On variable speed units, step up for service, then down for filtration. Always turn off the pump before moving the filter valve handle on the multiport valve. For flow context: Types of Pool Pumps.

Chemistry and water level effects

Backwashing removes water, so salt and CYA slowly drop. Re test after large backwashes and top up. Learn why stabiliser matters: Cyanuric Acid. Watch the water level so the skimmer box does not pull air on restart.

Step by step: how to backwash a pool

1. Turn off the pump. Confirm the filter valve handle is easy to move with no pressure in the system.
2. Set to Backwash. Push and turn the handle to the Backwash position. Ensure the handle locks. Attach a backwash hose if your services discharge above ground.
3. Turn on the pump. Watch the sight glass. You will see dirty water at first as sand’s ability to hold debris is reversed and the bed fluidises.
4. Flush until clear. Keep running 1 to 3 minutes until the water in the sight glass clears. This means contaminants and dirt have exited the media.
5. Turn off the pump. Switch power off before moving the valve again.
6. Set to Rinse. Move the valve to Rinse so the rinse process compacts the sand inside the tank and prevents dust from returning to the pool.
7. Turn on the pump for 20 to 30 seconds, then turn the pump off.
8. Return to Filter. Put the handle back to Filter and turn on the pump. Check the pressure has dropped close to your clean baseline and that water flow at the returns feels normal.
9. Top up water. If the level fell near the skimmer mouth, add water to the ideal height.
10. Final checks. Inspect unions and lids for air leaks. If you introduced air or lost prime during service, follow How to Prime Pool Pump.

Quick tips that prevent problems

• Highly advisable: power off before every valve move. Spinning under pressure can damage gaskets.
• Backwashing prevents long-term restriction, but regular maintenance should be based on the gauge, not a calendar.
• Left unchecked, a loaded bed increases head loss, reduces flow, and can push fines through the media, causing cloudy water.

Follow these basic mechanics and you will maintain quality filtration with fewer surprises.

Conclusion

Backwash only when the gauge tells you to, run until the sight glass clears, and always finish with Rinse. That routine protects the media’s ability to trap fines, prevents dust from blowing back into the pool, and keeps your system efficient. Pair pressure checks with weekly testing, clean cartridges correctly when fitted, and use Waste sparingly for messy cleanups. Follow these habits and your pool stays clear with less water loss and fewer chemistry surprises.