For those worried about the quality of their tap water but not yet using an ro/di unit, i would recommend placing a bag of a high quality carbon in the pail of freshly-mixed saltwater during water changes, before adding the water to the tank, for some peace of mind. This helps to improve water quality by absorbing if they are present, some of the heavy metals and removes gelbstoff (the compounds that give water in an aquarium the yellow tint), some large organic molecules,chlorine, pollutants and toxins, as well as many other types of chemical elements and compounds from the water that a protein skimmer or mechanical filter is not able to remove.