Hey Dylan,
The pic you posted when you first got it looks pretty average for a newly acquired rhizo... there is slight tissue recession on the bottom where some skeleton is exposed but that's not abnormal to see due to shipping. When you first got it did you dip in anything? Something I've encountered twice now is a very small hitchiker crab that lives on the skeleton that will actually crawl into the mouth of the rhizo and "steal" food from it - at this point the rhizo has already been irritated enough to the point that it cannot defend itself (i.e., eat the crab)... an iodine based dip knocks these guys off. These dips can also fend off bacterial infections.
Not to be a downer, but the recent pic you posted does not look good. Although these are generally hardy corals, I've only come across one like this before and the outcome was not good - a vendor here on RC called me up to come pick up a rhizo and save it for them, however it was in worse shape than yours is in the pics, but it did show the mucus development, which IME can be two things with these guys: 1.) The flesh is actually deteriorating and "melting" away, or 2.) The rhizo is expelling rotting food, which comes out looking like it's been covered in mucus.
Although these guys can eat a TON of food, they sure don't eat as much (in nature) as we can potentially offer in captivity. As with any "large polyp NPS coral" they can be overfed... they'll accept the food offered but don't have the ability to digest all of it before it literally rots inside of them. Undigested seafood + water is not a good mix over time. I would chock this up to potentially a couple things right now, either fed too much (they won't always spit it back up), or a bacterial infection. It's hard to say which one it is if happening over a two day period it's gone from looking like the "good" pic to the "bad" pic. Did it deteriorate rapidly or over a weeks time since you've had it?
At this point I wouldn't recommend dipping it - that or moving it would cause much unecessary stress for the (likely) little benfit. If it still accepting food I would try a few small pieces of Mysis shrimp, nothing more.
I've learned they are much "happier" with smaller more frequent feedings. I'll feed 5 "ish" P.E. Mysis or one Hikari krill every two days or so.
