To backwash a pool filter, turn off the pump, set the multiport valve to BACKWASH, turn the pump back on for 2-3 minutes until water runs clear, then switch to RINSE for 30 seconds before returning to FILTER mode.
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Backwashing your pool filter is a 5-minute process that reverses water flow to flush out trapped debris. Turn off your pump, rotate the multiport valve to BACKWASH, run the pump for 2-3 minutes until the sight glass shows clear water, then switch to RINSE for 30 seconds before returning to FILTER mode.
Critical safety step: Always turn off your pool pump completely before changing the multiport valve position. Moving the valve while the pump is running can damage the valve's internal spider gasket and create costly repairs. Wait for the pump to come to a complete stop before proceeding.
Rotate your multiport valve handle to the BACKWASH position. You'll feel it click into place. The valve should move easily - if it's difficult to turn, you may need to lubricate the valve stem or replace worn components. Make sure the handle is fully aligned with the BACKWASH label.
Turn your pump back on and immediately check the backwash sight glass or observe water flowing from your backwash line. Initially, the water will be dirty and cloudy as trapped debris flows out. Continue running for 2-3 minutes or until the water runs completely clear. For heavily soiled filters, this may take up to 5 minutes.
Turn off the pump again and switch the valve to RINSE. This crucial step settles the filter media back into proper position. Turn the pump on for 30-45 seconds until water runs clear from the sight glass. Skipping this step can result in cloudy water when you return to normal operation.
Turn off the pump one final time and return the valve to FILTER position. Restart your pump and check that your system is operating normally. Monitor your pressure gauge - it should read 8-10 PSI lower than before backwashing, indicating successful cleaning.
The best indicator for backwashing is your pressure gauge reading. When the pressure rises 8-10 PSI above your clean starting pressure (typically 12-15 PSI for most systems), it's time to backwash. For most pools, this occurs every 2-4 weeks depending on bather load, weather conditions, and surrounding vegetation.
Don't backwash too frequently - slightly dirty filter media actually filters more effectively than perfectly clean media. Over-backwashing wastes water and can reduce filtration efficiency.
Sand filters require the standard backwash process described above. If backwashing doesn't reduce pressure significantly, your sand may be due for replacement (typically every 3-5 years). Consider upgrading to ZeoSand or FilterGlass for improved filtration and longer intervals between backwashing.
DE filters require adding fresh DE powder after backwashing since the process removes all the DE coating. After completing the backwash and rinse cycle, add the appropriate amount of DE through your skimmer (typically 1 pound per 10 square feet of filter area). Use a DE scoop for accurate measurement.
If water doesn't clear during backwashing after 5 minutes, you may have channeling in your filter media or need to replace the sand/grids. For DE filters, broken grids can cause DE to return to the pool - inspect grids annually and replace damaged ones.
If the multiport valve leaks during operation, the spider gasket likely needs replacement. This is a common maintenance item that should be replaced every 2-3 years or when leaking occurs.
Backwashing uses 200-400 gallons of water per cycle. To minimize waste, stop as soon as the sight glass runs clear. Consider installing a backwash recycling system if you backwash frequently. In drought-prone areas, some pool owners collect backwash water for landscape irrigation, though check local regulations first.
Keep a log of backwash dates and pressure readings to establish your pool's pattern. Most residential pools need backwashing every 2-3 weeks during swimming season. Commercial pools or those with heavy use may require weekly backwashing. Always backwash before closing your pool for winter and after opening in spring.
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