The Bellus angel has ich, the other fish have ich (even though you can't see it) and your main tank has ich. If you qt ONLY the Bellus angel and put it back in the main tank, it will get it again. You need to qt all the fish and keep the main tank fallow for more than 6 weeks to be safe. There is no way around it. The other fish have the ich on there gills which you will not be able to see.