Other uses for tea tree oil:
Deters Lice, as well as other insects, and are great for carpet beetles.
Have pesky mold issue on the wall? Spray with a Teaspoon of tea tree oil to a normal cleaning size spray bottle. Whipe, spray again and leave. The mold will not return easily.
Tea tree oil may help incase of poisen ivey/oak
Tea tree oil on the nails will keep fungus at bay, and using tea tree oil will cure light cases of toe nail fungus.
-edit- and yes be careful of your bettas.