Backwash reverses the water flow through the sand filter to flush trapped dirt out of the sand bed and send it to waste. Rinse runs water in the normal direction, straight to waste, for 30 to 60 seconds. This settles the sand bed and flushes out loose dirt so it doesn’t return to your pool. Always do the rinse after backwashing, then switch back to Filter.
 

Table of Contents

1. What is backwashing a pool filter?
2. What is the rinse setting?
3. Backwash vs rinse: side-by-side comparison
4. When should you backwash?
5. Correct backwash and rinse sequence
6. Common mistakes to avoid
7. When backwashing stops helping
8. FAQs

 What Is Backwashing a Pool Filter?

 A swimming pool sand filter traps dirt, oil, algae and fine debris in a bed of filter sand as water passes through. Over time the sand gets clogged, pressure rises and water flow drops.

 Backwashing fixes this by sending water through the filter in the opposite direction. The reversed flow lifts and loosens the sand, and the trapped dirt leaves through the waste line. If you want to see how the filter is built and how the valve connects, our pool filter range shows the models and specifications.

What Is the Rinse Setting?

After a backwash, the sand bed is disturbed and some dirty water remains in the filter body and pipework. Rinse sends water through in the normal downward direction, straight to waste. This:

• Re-settles the sand bed so it filters evenly
• Flushes remaining dirty water from the lower part of the filter and the pipes
• Prevents cloudy return water that would otherwise blow back into the pool

Backwash vs Rinse: Side-by-Side

When Should You Backwash?

Don’t backwash on a fixed calendar alone. Use the pressure gauge as your guide:

• Note the pressure when the sand is clean (your baseline).
• Backwash when pressure climbs roughly 8 to 10 psi (about 0.5 to 0.7 bar) above that baseline.
• Also backwash if you see weak return flow, cloudy water, or after heavy use, storms, or an algae treatment.

For many pools this lands around once a week, but heavily used, tree-covered or commercial pools such as hotel and resort pools may need it more often. Avoid backwashing too often, because a slightly dirty bed actually filters finer particles better.

Correct Backwash and Rinse Sequence (Multiport Valve)

1. Switch off the pump. Never turn the valve handle while the pump is running.
2. Set the valve to Backwash.
3. Turn the pump on and run it for about 2 to 3 minutes, or until the sight glass shows clear water.
4. Turn the pump off.
5. Set the valve to Rinse.
6. Turn the pump on for about 30 to 60 seconds.
7. Turn the pump off.
8. Set the valve back to Filter, then restart the pump.
9. Note the new pressure. This is your fresh baseline.

Common Mistakes to Avoid

• Changing valve positions with the pump running. This can damage the valve spider gasket.
• Skipping the rinse. Loose dirt returns to the pool and the sand bed settles unevenly.
• Backwashing too long. It wastes water and gains nothing once the sight glass is clear.
• Backwashing too often. It strips the helpful dirt layer and wastes water.
• Ignoring the pressure gauge. Rely on pressure, not guesswork.
   

When Backwashing Stops Helping
 

If pressure stays high right after backwashing, or water stays cloudy, the issue is usually not a missed backwash. Possible causes:

• Old or channelled sand. Filter sand typically needs replacing every few years, depending on use and water quality.
• Oil or scale buildup that coats the grains.
• An undersized filter for your pool volume and pump flow.
• A worn valve leaking water to waste during the Filter setting.
   

In these cases, a sand change or a correctly sized upgrade is the fix. You can compare options on our swimming pool sand filter page, and read more maintenance guides in our blog library.
 

Final Takeaway

Backwash cleans the sand. Rinse settles it and clears out the leftover dirty water. Always run them as a pair, in that order, and use the pressure gauge to decide when. Do this and your filter will last longer and your water will stay clearer. If your current filter is struggling, explore the Pearl Water pool filter range, and browse more pool care tips on the Pearl Water blog.

FAQs

1. Is rinse the same as backwash?
No. Backwash reverses the water flow to clean the sand. Rinse runs water in the normal direction to settle the sand and flush leftover dirty water.

2. Do I have to rinse after backwashing?
Yes. Skipping it can send loose dirt back into the pool and leave the bed uneven.

3. How long should I rinse a pool filter?
About 30 to 60 seconds is typical.

4. How often should I backwash a pool sand filter?
When the pressure gauge rises about 8 to 10 psi above the clean baseline, often around once a week for average pools.

5. Can I backwash with the pump on?
You can run the pump during backwash, but you must switch the pump off before moving the valve handle to any new position.