thanks for your response. I had pretty much replaced every connection on the system, and since it was working fine on recirculate I determined it had to be something in the filter. Tonight I took the entire sytem apart, took all of the sand out of the filter and cleaned everything. I found some mid size clumps of something ( not sure what- maybe some hair and we have lots of cottonwood here from he trees and who knows what else) and a lot of small pieces of alge ( the water was green when we took the cover off) I repeatedly rinsed the sand until I could get most of the dirty water out. I replaced the sand, reconnected everything and the water flow is stronger than ever and steady. So I think I finally got it! thanks for eveyone's reponses.