RO/DI Ok for Betta ?

[Myka]

Personally, I would use dechlorinated tap water. RO/DI is quite harsh, and is ok in our saltwater tanks because we add a salt mix which essentially has a whole lots of minerals and elements in it which make it much more fish friendly. For freshwater, Kent makes a couple of great products called RO Right and pH Stable which work hand in hand to provide the minerals to make RO/DI freshwater fish friendly. Bettas do enjoy Blackwater Extract in their water, but you may not like the look of it.