I'm having trouble with my Cal Spa tub air locking. I find if I tighten down my filter cannister lid to the point where I can't hear any air tranfer then the main pump air locks and will not prime for me. If I loosen the filter cannister lid to where I can hear air tranfer then the main pump will prime for me but runs in a pulsating fashion. Can any one help me with this problem?? What is causing the air lock issue?? Could it be the pump itself??? This tub is a 95 model that I recently purchased used.