Yes, the process can be tough on both fish and fish keeper.
If you had Ick in your DT, then, you, MUST leave it fishless fir 72 days, there is no other way. No meds, no increase in temp, just no fish ( host)
Some fish show a immunity to Ick, this immunity is because the fish is strong, hardy or both.
Based on what I read, just stop doing anything except your normal routine and feed those survivors well.
As soon as you see the first sign of Ick, (smattering of tiny white spots) ALL fish come out and you start your 72 day DT fallow count down.
The fish go to a QT, uncycled, desktop light, heater, small HOB with sponge, same temp, hiding spots.
10% - 15% water change daily and add back the same amount of drops you took out.
It's math, so 30g QT, manufacture reccommend 1 drop per gallon, so 30 drops, every water change, at 10% would be 3 gallons so add back 3 drops.
At worst, you are learning, so don't give up.
If copper still worries you, fir Ick, Hypo works well and easy on fish.
Many of us have been in the same spot, don't give up, just move sequencially, that is only do what needs to be done.
Good luck!