Can I add a Red-Tailed Shark?

I am having a problem w/my Red-Tail Shark right now. I have 3 tanks.

The shark was raised in a 40 gallon community tank after I purchased him small from the pet store. He was fine for a while, but then my roommate started noticing him chasing around other fish after a couple of months. (around 4 inches long at this point)

We moved him to a 12 gallon tank and he was good for a while again. Then we added some black skirt tetras to this tank and he would constantly chase them around.

We added more plants and decor in the 40g tank and tried to put him back in there - hoping that he would find a spot and not bother the other fish.

Whoever said that this shark will not chase larger fish is WRONG. We have a very large tinfoil barb in this tank and it is SCARED ****LE$$ of the shark, who is 1/5 his size. When the tinfoil barb started ramming his head against the tank trying to escape the shark I knew he had to go...

But the shark is SO COOL. He is the sweetest looking fish I own. So rather than bring him back to the pet store i bought a 6.6 gallon bookshelf tank (ie: longer than wide or tall) and put him in it a couple days ago. I am hoping that he will be ok in this tank as the sole fish - people say he needs a 30 gallon tank minimum... but so far he seems to be happy... I got a sweet japanese palace decoration for him to live in, and he hangs out in there... he is emperor of his little tank.

A side note - this fish LOVES to hang out with clown loaches, and will not bother them. In the big tank they were buddies - he was like one of the crew (3 clown loaches). He also didn't bother my swordtails gouramis, or catfish. But the giant danios, tetras, barb... they were always swimming in circles trying to get away.
 
I've had my RTBS for over a year now. He's gorgeous and a real pain in the a$$. He's the only fish in my beautiful 29 gal because he became so mean and chased all his tank mates. :dog:

They really should be housed with other aggressive fish. I plan on giving him to a friend who has a 100 gal cichlid tank.

Hate to see him go. He's a fun fish to watch when he's alone.
 
I would go with a rainbow instead. They look very similar, but the rainbows tend to be less aggressive, and if they are given a cave to claim, usually content themselves to chasing other fish away from that area only. Do not plan on moving the fish on it matures--this will cause serious problems. My rainbow was happy with a cave, chased fish away from it but that was all. I tore down that tank and moved the fish into a larger setup, and suddenly he was a terror, harrassing every fish in the tank, despite having a number of potential caves. I moved him into a smaller setup with his old cave, and he moved in and settled down without any problem, ignores everyone else in the system.
 
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