I have never kept green terrors before so I can't really give you advice based on experience. However, they weren't named terrors for nothing. Whereas I don't think they're quite as bad as their counterpart, the red, they probably could be quite nasty. 75 gallons is not very big, if you've got two semi-aggressive fish in quite a small environment, it could be problematic. You will be better off going for a nonaggressive fish like three or four silver dollars for instant. I absolutely love my silver dollars, I would always have them. Blue Acara are also pretty cool.It's difficult to decide on what tank mates because 75 gallons is big enough for one Oscars, and just a few small tank mates so you have got to be carefully you don't go too mad because you will just end up with water quality problems