Flamming a is a waste of time, unless its really called for.
Op, 2 suggestions:
First, look on CL or any classified adds for a larger tank, you are very limited with a 4' tank, the pacu will be fine in a 125-150 for a little, along with the rest of your fish, if you HAVE to have more fish, look at dithers, like danios, tetras etc, SMALL fish that still give you movement.
Secondarily, if you have a pond put him in it now! If you keep him in your 55/75/93/ you will begin to stunt his growth.
I'm assuming your pacu came from much worse conditions and that's how you justify its current home, which is fine.
If none of these options are in the realm of possibility put him on mfk classifieds and find him a nice new home, no shame in growing a fish out then selling it!
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http://www.monsterfishkeepers.com/forums/showthread.php?504763-Cheap-plants-less-nitrate!-POTHOS
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