Stephen it sounds more like RTN, rapid tissue necrosis, than a bleaching. The few bleachings I've witnessed were a slower process and you could still see the polyps, albeit clear. RTN for me has been to look at a frag in the morning, come home from work to see it completely gone and covered in hermit crabs. I've never really tracked down the problem. I would buy 10 frags from a source, they would do well for a month and then out of the blue I'd lose one. I've heard all kinds of answers, not to say that any were wrong or that any were "the one", trouble is each time could have been for one or many of the answers given and different each time. Of course it's always prudent to check salinity, MG, and CA levels when guessing as to the answer. Other thoughts were that my supplements were poured in to quickly and suffocated the SPS that were in front of the return pump that blew the new mixture into the tank. I've heard that adding makeup water to quickly can cause them to fall out. What do you feed? If they are not getting any nutrient, if they need it, they could be starving and then suddenly give up. Are you rinsing the carbon and other chemical (I've never heard of Ultralith and have no idea what to do with it) as the fine particles could irritate sensitive corals. Has there been any sort of color shift in the bulbs, rapid degradation for no unknown reason? Are you sure your lighting is working for the set amounts of times, no problems with the timers? Is the tank getting hot at any point of the day? Any predation issues?

We've all had RTN troubles. I've not had a simple answer. I wish the best of luck with what remains. I can probably replace any cap that you lose with frags.