can you put hime in his own tank with a couple of cons or somthing he can't catch but still be the dominant fish, that could work also.
purplecandle;4791043; said:Don't know if this will help, but I found this while looking through the media section. Seems someone had a similar problem and he believed it related to temperature..
http://www.monsterfishkeepers.com/forums/showthread.php?t=382036
greenterra;4791506; said:It could very well be a dominance issue as stated already. Maybe a dispute you weren't there to witness? I would let him go for a while and see how it pans out. I would not introduce a female to the tank as it will usually induce aggression. Maybe in time he can find a central position in the hierarchy so he still feels dominant.
The second would be food IMO. If what you are feeding is different to his previous diet, it could have diminished his interest to eat. My midas does this all the time. The nights I feed Hikari floating pellets, he is at the top smashing them with gusto. The alternate nights I feed Masivore, he sits back at the bottom while every other fish is eagerly feeding.
Temperature is the third thing to consider but as Aquanero said, increasing temps can also induce aggression which brings us back to the dominance issue.