Pump Speed For Backwashing Sand Filter


New member
Aug 16, 2020
Olympia Washington
I'm running my two speed Hayward 1.5hp pump on low speed 24/7. About every two to three weeks, despite no visible rise in the roughly 5psi filter pressure drop reading, the flow falls off to effectively nothing. If I then put the pump on high speed, I get good flow again. Once I backwash the filter it's good on low speed for another 2-3 weeks. Does this seem normal?

Also, should I be backwashing my sand filter with the pump on low or high speed? On high speed I see sand in the sight glass and the sight glass leaks a little bit. I also get a little bit of sand out the discharge pipe. Which makes me wonder if I should be just using low speed for backflush.


TFP Expert
LifeTime Supporter
May 3, 2007
Pleasanton, CA
Pool Size
Salt Water Generator
You should always backwash on high speed. Also, when determining when to clean a filter, use the high speed filter pressure and clean the filter after a rise of 25%. Low speed filter pressure is not very accurate.

What size is your pool and what size is your filter?

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