I'd stick with him, add some floating plants; it'll give him a little shade. If you persevere, high chance he will come out of his shell and become a brilliant wet pet
That is sad and disappointing:/
My first thought is to suggest bold dithers to bring him out more, or maybe a companion?
He does look stressed, but appears to be healthy. I'm really not sure why your boy would be acting the way he is.
Sounds stressed.
Let's cover some basics:
Water temp? 28deg C [or was it 30? oops. shall get home and check]
Nitrate levels? [shall check] [Filtration is 3 canister filters]
High flow or low flow in the tank? [High flow. Flow directed back to front, slightly angled upwards]
What's the stock like? [GT, Salvini, 9 Clown loaches, 2 Yo-Yo loaches, 2 Royal Plecos, 1 Flash Pleco, 1 Butterfly Pleco, 1 Green Phantom Pleco,1 Clown Pleco and 1 Bristlenose Pleco [Plecos are all Juveniles except the Butterfly]
What is his diet like? [Hikari Sinking Cichlid Gold, JBL Cichlid sticks, Hikari Sinking Carnivore Pellets, Hikari Sinking wafers, Tropical Krill Chips]
Any flashing or poops that look off? [Flashin? Poop is usually red in colour like a hikari food stick]
Any signs of illness? [Not that i can see]
Where is the tank located? High traffic? [I guess. It's in a space between two rooms]
Picture of the full tank? [Posted above but shall get a new one tonight]
Big robust cichlids that spend all day in a cave just isn't right. My gt is at the glass 90% of the time watching us and or begging for food. [He does that when he wants food that's all]
love Green Terrors, nice specimen you have there
Your definitely on the high side for temps, like the max. I would aim for 75-77 and see if that changes anything. Is the salvini being aggressive?
Flashing is when the fish flicks off of substrate wood or plants or the side of the tank. Like scratching himself. It's often a sign or irritation.
Dithers could work just make sure you don't add too many and create a situation where your nitrates will be out of control. Ensure the gt can't eat them. Also make sure to QT the new fish to ensure good health before adding them. I would suggest a wide body tetra or a giant danios. The together barbs could be nippy and are very frantic.
The higher temps could lead to lower oxygen levels, any heavy breathing?
Odd question but do you have anything red that is near his tank?
I'd add duckweed, it'll grow steadily even under medium light.
If you add a female GT, you may just see an entire character change; at the expense of other tank inhabitants.
I'd avoid tiger barbs, they'll get smashed. If any dithers, I always preferred giant danio's