Water changes, several smaller changes are less likely to stress the fish in my opinion.
I will agree to disagree with Flower, I don't put anything in my tank, I try to control all situations as naturally as possible.
I just went through this with my QT tank, trust, me diligent with the water changes, be careful what you are feeding, and you should be able to get through it.
It sounds like the tub is going through a cycle, what you are going to do is to allow this to happen while dilluting out the amonia to a liveable level to the fish. The last thing you want to do is to further stress them out, especially with ich present. You will likely slow down the cycle but the fish can make it though.
Are you performing hypo?