When you deionize water you get ride of both foreign ions, such as Na(+1) and Cl(-1), and any EXCESS OH and H3O. You will always have some OH and H3O that you can't take out. I work in a Nanofabrication facility, so I get my water from here. The DI water system we have takes water to 20 MOhms and higher (which pretty much isn't conductive at all). Thats some pretty clean water! I have been using it for all my water changes for a couple years now without any problems.