When it happened to me I water changed every day, cut my losses on whatever looked super bad, and iodine dipped a lot. Honestly cutting my losses on some pieces is probably what save the rest of the coral. Do not let the flesh float away in the tank, that is what spreads the infection. You need to either siphon out or cut the head/branch way. Recommend shutting off flow while doing this. Hopefully someone really knowledgeable on BJD can help more. Sorry to hear about your situation, best of luck.