What gets along with tetras?

[frankinator]

Hi I have a 20 gallon tank I have a catfish and 3 black skirt tetras, and four white skirt tetras, I am looking for suggestions for what other types of fish that I could add to my tank, thank you

[talldutchie]

I can throw you 3, 4 dozen names but none might fit.

How about a bit of information here? Which catfish? What's on the bottom of the tank? How's the decor of this tank? Is your water very hard?

[steeler58]

And your black/white skirts have already taken up most of the room in your tank, they get a lot bigger than most people realize :(

[SueD]

And... is this a 20 long or high?