Mark,

I meant 1/2 gpms of the high speed pump not 1/2 gpms total. My bad for not clarifing that. I was guessing a low speed rate may act like a dirty filter.

I understand your explanation, and believe the dirty filter is the problem.

My system is a Fafco Sun Saver 5- 4x12s panels.

pump- Waterway svl56 1hp 1.25sf Clean Filter Solar Off PSI 14psi
Clean Filter Solar On PSI 16psi(17psi at first, then drops to 16 when all air is purged)
Dirty Filter Solar Off PSI 20psi, time to backwash
Dirty Filter Solar On PSI I need to verify this reading.

Thanks for looking at my numbers.

P.S. I agree with Cleancloths with the STICKY recommendation.

Joe