+1 with eco23. Bala sharks should be in a 125gal minimum ... they grow to a foot and are VERY energetic sharks that need room to swim.
An RTS matures into a VERY territorially aggressive "shark" IMO a 75gal (I used to say 55gal) should be the minimum AND then there needs to be territories set up for it to claim ... i.e. plants, caves, decor etc. Even then ... there's no guarantee they wont terrorize their tank-mates.
My RTS (a gift for my son from his G-father) is in a planted 75gal with plenty of "territories" and it still pretty much claims the whole tank as it's territory. I'm convinced that for now it's willing to tolerate it tankmates, but at 3 inches, it still has another 3 inches to go ... and it if it gets too aggressive, I'll have to rehome it.
Rainbow Sharks are not as territorially aggressive ... but it's basically like a slightly smaller, more docile RTS ... needs a 55gal at minimum.