there is a fish shop in my area here in Southeast Asia which has a big all glass tank with dimesion around 300 cm x 120 cm x 100 cm, and there were some goliath fishes like yours in the tank. The shop is visited by many people everday, and lots of people are stopping by in front of the giant tank. And even with such a big dimension like what they have, I still notice some bruises on the fish's noses (goliath) and some even delevop a tumor like around the same area. Maybe both sides of the tank could be painted to prevent them from smashing the glass, but dunno if its gonna work. Anyway, bigger space is always better.
cheers