I have generally found Kent products are good. The instructions say remove corals and invertebrates, however, which means they will come back in with some chance of bringing the ich parasite back into your tank with the water that surrounds them.
The best thing to treat ich is to take the fish out and keep them in a treatment tank for up to 8 weeks, having NO fish in your main tank. This means the parasite will not have a host fish to complete its life cycle and it will die out in your tank. Your fish will have been treated to eliminate the parasite on their skin and gills and they will be free of it, too.
The difficulty in using RXP in a hospital tank is that you would have to move your skimmer to run the hospital tank, as RXP uses the skimmer to reduce its levels gradually. This is probably not practical. Hyposalinity is a good treatment for ich, and safer for the fish. If you have them in a hospital tank, this is easy to do.
If, however, you opt to remove corals and use RXP, you should, I think, set up an intermediate 'bath' of clean salt water and dip corals vigorously in that before transfering them to a holding tank---which must be filtered and aerated and lighted, by the way, for the corals. The intermediate 'bath' going and coming is one way you might be able to clean them of parasites. Hmmn. There are also some dips, like Lugols, that are routinely done for coral pests. They might be quite effective on ich, for just the corals. So you might make your intermediate step a Lugols dip. Not for the fish, however!
