Firstly.... Respect for you making a tough decision...
However, I am also a responsible fish keeper and hate seeing fish mistreated or squashed etc, but I believe that if you have a typical 180 @ 6x2x2 then a hystrix will be fine, they do not get big at all, I would probably not get any ther bottom dwellers so they can have the floor to themselves, then just get some nice middle n top swimmers.
There will always be somebody that tells you that you need a 1000g tank for a Oscar and 50 fx5's but in reality you can generally judge if a fish is too big for is tank. Again I applaud you for accepting that a fish is too big for your tank, which is something too many people don't do, hence you see oscars in 2ft tanks etc, I just feel like you may have been a bit rash
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