[RussellTheShihTzu]

If there was a reptile in that tank you need to really deep clean before adding fish.

A 20 high would be fine as a community tank. You could have a shoal (6+) Cory for the bottom level and a couple of shoals of Nano fish for the middle level. If the male is a long-fin, avoid Neon Tetra as they can be quite nippy. With the female they would be fine.

 

[RussellTheShihTzu]

So sorry, I didn't see that you had responded.

Always have a back-up plan as Betta can be unpredictable. Not usually; but possibly. In 40+ years I've only had a few Betta that did fine in a community setting for a while and then didn't.

I like Habrosus/Salt and Pepper Cory because they are smaller. Panda, Albino, etc., are also nice.You have a lot of great choices for tank mates.