It looks like bacterial infection or something. I cannot tell what it is, but I would pitch it to save the other frags you have in your QT tank. I hope you can save the other remaining frags.
Buying from other hobbyists online/long distance can be somewhat risky. I suppose you have found out about this unfortunately the hard way.
The experience I had (purchasing/trading) with other hobbyists were kinda mixed. A number of them did not even know how to pack livestock well. Some coral pictures people post may be photo-shopped up, too. After a few disappointing purchase/trade, I decided not to do this any more unless I know the source really well. YMMV on this.
We have pretty good LFS around here. All livestock I bought from our LFS's (CRA, Lucy's, The Aquarium Shop, Living Reef, Aquatic Critters and Aquarium Designs) have done really well in my tanks.
By the time you pay shipping, the cost is about the same as buying from LFS's. Frags are definitely cheaper from LFS's.
That said, I am still tempted to purchase corals from a good vendor such as Reefermadness occasionally (I have not done that yet.) The group buy we did a few years ago with the Sea.org was successful. A few of us might get together on buying something together in future if anyone wants to do so. I see other clubs are doing this periodically.
Tomoko
