Long ago when I was dosing vodka my water ended up being "too clean" for my zoanthids and they didn't like it at all. The SPS loved it, the zoas not so much. It's basically a lack of nutrients, good nutrients that some corals use for food.

As for the RO water discussion, if you don't have one spend $100 and get one. It's what I would consider one of the absolute necessities of this hobby. Unless of course you have a nano tank, then the wal-mart distilled is what I like.