Get a copper test kit!
It is very important when using copper.
Be very careful and pay close attention as you can kill your fish faster with copper then many other meds.
Ich in marine is NOTHING like freshwater.
You need to keep tank free of fish for at least 1 month as marine ich can live without host for over a year in some cases.
Don't raise temp either(not good).
***ICH: HOW TO TREAT: Marine ICH(cryptocaryon irritans) - Reef Central Online Community
post 2 in the link is BEST info on marine ich.
you can add inverts or rock if you choose.
good luck(never heard back about your sump in other thread?)