I know this has probably been asked so many times before, but i am a little confused with this RO water "v" tap water. I was told before i even got my 200lt tank that tap water would be ok as long as i tested it before use and all was ok. I have now just been to me LFS and been told i should not be using tap water at all at it kills the fish. i am lucky in the sense i have no fish in my tank yet as i have only just started and was about to add the live rock and sand. However now i am wondering if i need to do a complete water change using RO water??? Your help with this will be muchly appreciated.