I have three zones that are running at the same time with low water pressure to all three. This is a new problem. Any ideas on hat might be causing it? 

So far I've tried replacing one solenoid, that did not work. I switched the zones in the control box for one of the three zones but the same result when I activated the switched zone. 

I also tried disconnecting one of the zones, and when I triggered it it did not run. But when I triggered one of the zones I left connected, it did run with low water pressure