Agreed, that's not brown jelly.
You will know if/when you have an outbreak. One day a given LPS coral will be all happy and extended. Then you come home and it's polyps are retracted and within a few hours there is this brownish colored mass covering the polyp(s) and the coral is sucked way into the skeleton. It's a fast killer and can decimate a coral colony in days as it is highly contagious.
I have had corals that were happy/healthy for well over a year or more and then within a 9 hour span be dead. I used to try to save them with dipping in Revive, iodine, RO rinses, etc. Nothing I have tried has managed to save a coral once it is stricken. The best I can do is break out the dremel and cut off the inflicted polyp(s), iodine the remaining and hope for the best.