Paralyzed Glowlight Tetra

[primeus22]

I've had my glowlight for a few months. He's grown big and is on of the bigger fish in my tank, but about two days ago he just started laying on the ground on his side. I tried seeing if he could move by seeing if he would run from the net but he just lays there. He is still breathing and i think he eats but he can't move his back fin and the people at the pet store didn't know what to do either. the only medication I've done before is Maracyn for one of my fishs with pop-eye who later died, i have changed the water since then though.

 

[WILDER]

Size of tank in gallons or litres.
How many fish and which type.
Water stats in ammonia, nitrite, nitrate, and ph.

Does he look bloated.
Are scales sticking out.
What does it look like when he goes to the toilet.
Does he look pale or darker in colour.
What do you feed the fish.