Could I add more to this tank (20g)

[Tropical]

Black neons and neons are different species, they won't school together.

I have both gold neons (blue lined albino neons) and regular neons, and they do school together but the problem is, they don't look good swimming together. I wouldn't recommend it, it kinda ruins the visual effect.

Good to know about the gold neons, I'll stick with the julii's for now.