My GT is only 3". When I put him in the tank...he was nervous, surrounded by 2 Convicts, 1 JD, and etc. New tank and environment always make a fish nervous. Give your GT some time...with the tank's light off. The GT will start to feel a bit safe. My GT didn't start eating like a horse until 3 days being in the tank. Give your GT very small amount of food first couple days. I gave my GT flakes the first day...he ate couple only. When I noticed him actually coming to the front of the tank every time I got near...then I know he was ready for a big meal.
If you want to make your GT coming out more...get a dither...like Giant Danio. I have couple in my tank. When my JD and Cons first got in the tank...they were so scared until I put in the Giant Danio. The Danio seemed to calm them down a lot.
GT isn't very aggressive. I don't know what's the chances someone will get a very aggressive GT. All the GTs I owned...they are mild temperament. In fact, the one I have now...he is scared of the male Con who is an inch smaller than the GT. However, GT gets very beautiful when they are fully grown.
I hope I've helped a bit here.
Good Luck with your new GT.
