Well, mine is still being weird. I put him in the brackish tank, which did nothing for him, so I added another tablespoon of salt this morning. He almost immediately turned white and started nipping at the surface, though still ignoring the krill I tried to feed him, then shortly after turned black again.
Like I said, he was black bellied when I got him. He has now been in three tank environments; the pet store (don't know what they used), my freshwater tank, and my brackish tank. None seem to make any difference, so I think odds are that he has some kind of illness or parasite. He did seem to bloat up a bit yesterday even though he was in the brackish tank alone, not eating anything. I am leaving for a 4 day vacation later today. Anything I should get and put in the tank he is in now (back in freshwater) that may cure him while im gone?