Yesterday I bought a Betta for the right side of my newly divided Betta tank. He had been at the store for quite a while. He had bad fin rot so they moved him to a 0.5 gallon filtered but unheated tank (obviously it still kept getting worse). I have also never had a divided tank and he got past the divider and got beat up by Neptune (the other Betta). The new one is obviously weak and did very little back to Neptune. Sadly this happened during the night so they could have been fighting for hours. So far they have shown no interest in fighting so far today (they are on their own sides now and haven't tried to flare or get to the other side). I think I figured out where he got through so I will fix it. In the second picture I drew lines where his fins were before the fight in case that could help. He also has fin rot on his pectoral fins. Should I do anything else other than keep his water clean and warm? He is in a divided 10 gallon with a heater and filter. I fed him last night and he ate one pellet. He wouldn't eat anything this morning.