Hopefully it works hun.. I would say it may be a temporary solution, some fish are just more susceptible to ich then others, which is why you probably didn't get it before the molly's. Ich is usually caused by stress, or bad water parameters.
Although, after treating fish for ich and they recover, they do become somewhat immune to it.. so it will be harder to contract ich again. Not saying that they won't get it again, just that it would be harder for them to get it again.