Ahh they need space to swim, they are hyper guys! I would say the shape of the tank is more important than how many gallons. Like a 20g long is better than a 20g high. They need groups of 5-6 or more, as they tend to he territorial and a bit aggressive in small groups. Other than that, great fish to have. Very hardy! Mine were in a 5g tank when I got them. I would say anything 24" and longer would be a good size for them.
Hey, I see that you keep danios... I was wondering about the care reqs for them? If I understand right, glofish are the same species but genetically modified... adn I'm kinda interested in getting some. lol (in a seperate tank, seen my grandma's danios and I know they're fast buggers)