My New Arowana!

Picked this guy up today.
Only 4 inches long. In a tank with a 5 inch red devil, 7 inch Dempsey, 3.t inch Green Terror, 2 inch p.Managuensis, 2 inch Dempsey, and a 4inch Black Ghost Knife. Talked the LFS owner from $110 down to $55! The terror and small Jd are my friends and I'm keeping them for a short time while his dad battles lung cancer. He should get them back in a week or sooner. I'm trying to find a home for the devil. Preferably another tank at my house if my wallet will allow it. I'm keeping the JD and the BGK in with my Aro. JD doesn't mind other fish, just no other JDs that might be competition. Here are pics if the aro!
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From the pictures, does it look like he may be developing some fin rot? You can kinda see at the bas of the fins it is yellow, then it fades into a grayish blck and the very tip is whitish. I noticed it today. Im going to do a big water changer and add some salt tonight to be on the safe side. Any ideas. Ill post new pics (from today) in a minute (24 hrs after the first pics were taken).

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