No but there is so many chemicals etc in tapwater that everytime you do a water change you will be adding more of these to a closed systemUsing Tapwater (depending on your area) is not a good start to any marine tank
You will simply be increasing the phos levels ever time you do a water change
Agreed, tapwater is a HUGE no-no. Also, what kind of lights are you running on the tank?
I also use tapwater and there is no way that I could ever get RO water. Will my tank explode or something?
You will also be fighting an ongoing battle against nuisence algea, due to it being fed by the phosphates in you tapwater
Why not buy a RO Unit, they are cheap as chips & also very handy to have incase of any problems where you need Ro right away