You know, I had a similar situation as this about a month ago. My Doubletail HM Butterfly jumped the barrier into my Crowntails side of the 10g. Took a good beating. I am really surprised that your little guy is acting so normal. Mine DTHM was depressed for a week, and the Crowntail stressed himself to Ich. It is good to see that you have such a little trooper.
In all honesty, I think it's just keeping him company that's helped. He's a very friendly little guy and he loves human company so I check up on him every hour and spend some time just chatting to him and he chats back (obviously can't hear anything but the occasional click!). Such a sweetie 
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