You dont need the melafix, IMO/E. Just keep his tank clean with very frequent changes and if you want add some AQ salt, 1tsp/gallon for no more than 10 days.
If you have a filter and its not cycled, shut it off to promote better, faster growth.
He just needs some tlc, not meds. Especially if he's a chronic biter, because you can over medicate him.
Try adding cool, interesting things inside and outside the tank. I put pictures up beside the tank and you can try putting unconventional objects inside the tank, so long as they are non-toxic and child/pet safe. Many people put children's toys in that have large openings to swim through- though the size of a quarter and up holes are a must.
And okay, just wanted to check. Ive been seeing so many very young males latley that I just dont know anymore! Theyre cute. Do they get along well? Just asking since Ive heard 5 is better than 4 sometimes. But if it aint broke, dont fix it, right?