I have heard this many, many times - but is it true? My experiences when dosing copper in a tank with limestone is that in a week or so - it has totally disappeared from the water column. The same will happens the second time, the third time and so on. Zero in the water - all in the limestone. Never seen it coming back into the water column. Why should it come back? If it is true that it will dissolve back - systems that have been treated many times - you will not need to put in copper - the limestone will fix it. Never seen that. Is there anyone that no exactly what´s happen? @Randy Holmes-Farley - do you know?Your live rock most likely absorbed some copper, which means they can release it back into the water, pretty risky to add corals to that. Rocks absorbing medications is the reason you don’t use them in QT
Sincerely Lasse