once the flesh starts deteriating, you need to do iodine deeps in special solution probably once a day for the first days untill he looks better, and after that only when the bubble doesn't look good once a day. but because it's so far gone, there is a possability of it not to be able to recover. lots of reefer maybe will tell you that deeping is too stressful, but when i wasn't good with keeping my water good and when it bit me in the butt, the iodine deep pulled my bubble coral and lots of xenias through. also assure nice flow but not too much over the bubble, so everything that is sick will be blown away from it. remember that once the bubble has any live tissue left, the new bubble coral will be born from it.