OK. I also read your separate thread on the dead QT fish. Sounds like they had a disease and were too far gone for your copper treatment to matter. In any case, that sucks and I'm sorry. I hate losing fish.I was using a brand new Hanna checker. I hadn’t even gone above 2.0 when the fish died.
Let's see what the ICP testing shows. Maybe one of your pieces of DT equipment is leaching something into the water.