Here is some basic info I posted here earlier bro:
http://www.monsterfishkeepers.com/forums/showthread.php?t=86138
My .02
Ok....
Here is my personal experience with Grammys......
a 55 would be fine for a permanant home as a solo fish, They do not get big, they are mean, I had a grammy that I gave to a friend (3.5") take out a 7" Jag....They need their space.....Slow growers....Ive seen a few, but polomax. bigkill, and darthodo have the best ones I have seen (adults). I have one who is in a grow out tank now (The runt of my 7 total) and the only one left, he will be joining a gen pop of similar sized Festae, Trimac, RedTexas, RedDevil, Barred Midas (all juvi) in a 220 gallon tank. Take care of that fish and you will be rewarded, mine were very skittish at first, but I have had them (I have only 1 left) for 6 months, and he is now very responsive to me....now....before, I was irritated, as I got no response.....I have been rewarded with a 2" stone cold killa.....Great fish....The reason I got rid of the rest is they were hyper dominating my 125, started out ok, but slowly they took over from fish 2 times their size.
I will recommend that you break up the "Speed Lane" of your tank, ie: put some driftwood or rockwork in the middle of your tank to stop/slow down the ability of these fish and their "quick strike" ability, as they will streak across the tank building up speed to attack their prey/target(s). Breaking up the middle slows down the ability to fast track and kill a target fish. I learned that from a very experienced fish keeper in the GCCA who gave me feedback on my old 125 and what I could do to stem the aggression of these fish....
Thats my experience, good luck and I wish you well, they are rewarding fish to keep......
IMHO
Chris