Hi michael999,
Basically, think of a shallow marsh. The following is an excellent picture of where a wild betta would live.
http://www.myfishtank.net/forum/showthread.php?s=&threadid=23693
Bettas like surface space, so a wider, deeper, flatter tank would be the best setup. Deep tanks are wasted on bettas.
What I suggest is about a 20 or 16" wide x 12" deep x 10" tall tank (approx US 8.3gal) Basically, a short 10 gallon.
Design considerations:
- Footprint size: Make it as wide and deep as you can fit in your space/stand.
- Height: Make sure its just tall enough for your filter and heating system.
- Filter Size: I would use an
ELITE Mini internal filter on a low setting. It's only about 4" tall and would keep the water moving just enough not ot bother the betta.
- Heater: A 50w submersible on it's side would be nice.
- Substrate: Consider using sand, it looks much better than gravel.
- Decoration & Plants: Driftwood covered in java-moss and Javafern for height (or dwarf swords) You might consider letting the driftwood come up out of the water a little and use some floating plants, like frogbit or duckweed.