In my opinion, RO is not good for most species, unless you buffer it with something like baking soda. The lack of buffering using straight RO can cause many problems.
The only species I would use RO with would be something like Uaru fernadenzeppizzi, wild discus, or other species that come from totally minerally deficient areas, and even then, i would add a little baking soda, or tap water that has been inundated with tannins from leaves, or some other tannin source.
I doubt that with the fish you (OP) are currently keeping, RO is a good thing, unless your tap water is somehow tainted.
I believe if you go to your city''s drinking water quality report there is a wealth of knowledge on it to help you determine the reality of your situation, and you may find your best option is simple using and dechlorinating your tap water.
If you do go to the sigte, link it here and someone here may be able to point out the way proceed.