We have a have a 5 pool pump water circulation system running in parallel, that supplies water to 8 test bays. 3 are plumbed close together. Well, lately pump 1 has started to cavitate to the point that it caused the pressure side piping at the pump union to swell. Although, if you run pump 1 by itself, it runs perfectly. It’s like pumps 2 and 3 are starving the supply water from pump 1. Note: The supply water comes from large tanks that are suspended on racks above the pump system. Could there be too much suction pressure coming from the water tanks? I am at a loss and I need to find out how to stop the problem. Thanks for any advice.