Copper issue ?

[Markdickenschwanz]

Hello all, sadly the majority of my LPS and leathers have and or are perishing (aside from some tiny feather dusting looking things) this has been a long term (1 month) issue. Both of my fire shrimp have passed on as well. Purchased Hanna high range copper checker. Tank was running at .21 and RODI not registering at all. All other paremeters are fine. Salinity 1.025, alk 8.6, phos .04 (and that's me dosing) ph 8.2 though nitrate remains high at 46.6. From my understanding that amount of copper shouldn't harm the invertebrates. My furnace did blow though 3 months ago where hot and cold were mixing for awhile. That has been the only anomily that I can associate with this predictament. Hammers were always shy about coming out but frogspawn just loved to do his stuff. Toadstools and mushrooms were also well and thriving and now just shriveled up. Anybody steer me in a direction to solve this would be greatly appreciated.
Tank has been up and running since March. Water supply is well water. DT is 125g, 20 g refug with 15g sump

 

[Ben.QLD2]

They all died of copper poisoning. 0.21 (ppm I assume) is nearing therapeutic range for some treatments. You need massive water changes and carbon.

 

[Tamberav]

Check all your pumps/magnets