Sk3lly
Aquarium Advice Addict
Remember the 1 inch per gallon rule. Neon tetras grow to about 1 1/2 inch long, so I would have maybe 4 max. I wouldn't put male betas with other fish.
Bad rule to use. Very outdated. An example why its a bad rule. Black ghost knife fish grows to 20inches. A 20 gallon tank enough then is it?