I've started a new job at the hospital here in town. It has roughly 200 heat pumps in the facilities. Recently, I've been working on cleaning out a coaxial heat exchanger on a 2 ton system. The hose kit and heat exchanger have had some sort of scaling inside them that restricted flows enough to cause the loop's delta T to be 20-24 deg. F. in the cooling mode. The pressure drop across the HX was 16 psi. After flushing the HX and cleaning the scaling from the valves/hoses, it now has a pressure drop of 7 psi, and has a loop delta T of 11 deg. F. We know the scaling is metallic -- it can be picked up by a magnet. I have a few questions on it: 1. What would be the likely culprit of where this scaling/residue/deposit/corrosion came from? 2. If it's corrosion, what might we do to stop it? How might we know if it were corrosion vs. contaminants just left in the system? 3. Is there a procedure you would recommend on cleaning each heat exchanger of this scaling--more than just flushing water through it. In the past, an engineer recommended muric acid (or muriatic acid, I can't remember which) for cleaning a heat exchanger. However, that was for a Domestic Water heat exchanger that was using well water... Any help is appreciated. Thanks.