I do 100% water changes based off a recommendation from Copps. Not to mention my water parameters in my QT are always exactly the same as the ones in my 250 gallon tank(370 gallon system). My water change system is plumbed so that the waste water from the main system pumps into the QT and the QT overflows into the drain. I do water changes every 3 days so my water quality is extremely stable. This allows for a super easy adjustment from QT to DT, not to mention makes 100% possible due to literally identical temp, salinity and PH. I will have to run a copper test when I get home.