How big can I go while keeping the same light?

[TheReefGeek]

How well is the flame doing right now in your 20g nano?

I think you said the flame was full grown so you can't stunt its growth.

I do agree 36" would be much much better for this fish.

Bigger is always better.

And if you are going to do 24x24, at least you can help it with some good aquascaping so it doesn't have to swim 24" and turn around and go back the same way. In my 36x18" tank my coral beauty would rarely swim the length of the tank, I had a big arch in the middle, so it mostly did figure 8's.