Join Date: Oct 2010
Location: Victoria, Australia
Do you know what kind of parameters your tap water (assuming you are using tap water) has?
You could try a small school of ember tetras (around 4-6). They do not grow very big, but do prefer softer water from what I have read. Another option is one of the small native blue-eye (pesudomugil) species. However, their darting movements and sparring between males may encourage a betta to attack.
Otherwise, it does depend on your male's temperament. Some male bettas are extremely aggressive to anything, while others are a lot more placid.
Also, the smaller schooling fish may need a smaller pellet or for it to be crushed up first as they only have small mouths.