All the inverts can stay in the tank. Only the fish need to be removed. The ich virus only lives on the fish for a few days (max 7) and then drops off to hide in the sand, rock or whatever and multiply. It then rehatches in anywhere from 3 days up to 28 days, when it hatches in needs to find a fish within a day or so or it will die. That's how you break the cycle, if there's no fish in the tank when the ich "hatches" it dies off. You need to wait at least 6 weeks because it can stay in the multiplication stay for up to 4 weeks before hatching. Good Luck, I just finished with a same thing, (fish out of tank for 6+ weeks and in QT with cupramine) fish have been back in the tank for 3 weeks now and everyone is healthy and happy.