We recently changed the hot water heaters out. They were in series with a recirculating pump. The one with the pump attached was easy to drain but the one that was the intake for the returning hot water was full of blue green crystal. The hot water pipes had this same colored film on it but the cold water did not. All my research wants to lead back to electrolysis. If this was the case, unless it was the pump itself, wouldn't all water lines be affected? Do you know what the cause could be and what the fix is?