ok, hold the phone...
let me clear a few things up. your tank is now a copper tank, always will be, even if you were to clear everything out and replace it all, the copper has infused with the tank itself. just ask anyone who knows metalurgy or even better, semiconductor assembly... Copper is one of the most invasive and impossible metals on the face of the earth. it is nearly impossible to remove and you will always have a risk of copper poisoning your inverts. time to look at a new tank system and turn your old one into FO or QT.
...copper sucks in general...
To treat ich effectivley you need to look at the cause. A fish will not catch Ich unless its immune system is damaged from stress. stress is usually caused by a parameter in the water being off. look at your water quality and see if it may have a problem... PH, waste, phosphate, ammonia, nitrogenous compounds, temperature, and salinity. if you fix the water the fish will usually kick the ich on their own and get better. if you add some garlic to their food it will boost their immune system and help them kick it as well.
good luck and sorry to hear about the problems.