At the monent I have pangio kuhlis (striped) and Pangio javanicus(black kuhkis that are really dark brown

) I find Pangil kulis to be tiny(like thread like tiny) at first. The Pangio Javanicus are a little chunkier but both will be fine as long as they have places to get away from the Betta.
The texture of tahitian moon sand would be great but isn't it dark? would you be able to see the kuhlis?
Once you've had Kuhlis you will be hooked for life. They are really funny fish.
Here are a couple of pics for you

Carol