Reading through this thread I can see at least two misunderstandings. The first, which others have noted, is the mistaken idea that salt is somehow a disease preventive, it is not. Salt can be an effective ich treatment if your fish are ones that will tolerate the needed levels. Another misunderstanding is represented by two actions. Moving fish to a separate location for treatment of ich is worse than useless because ich is a parasite that cannot be treated when it is on the fish. It is treated in the free swimming phase of its life cycle. The ich parasites regularly leave the fish to continue their life cycle and shortly after are vulnerable to treatments. Unfortunately there will be no signs of ich on the fish for several days before the treatment can be stopped. Otherwise, the parasites will again find a host and the tank will look like it is having a new outbreak. For this reason, you always treat the whole tank where the outbreak has happened and you continue for at least 3 days after the last sign of ich is gone from the last fish in the tank.
Where you have placed yourself so far is with an effective treatment started in a separate tank but nothing to stop the rest of the fish in the original tank becoming infested. The salt levels you are using in that tank are not high enough to prevent a new infestation of the remaining fish from the free swimming stage that is likely present in that tank right now. You need to do at least that 3 day treatment on your tank and may find that you are too late anyway and see spots appear in your remaining fish. For details on the ich life cycle and the disease treatment, use the link in my signature area called Ich Info. I have merely summarized a few key points here in this thread.