Title says it all. I am aware of the pitfalls when it comes to marine tanks and tap water and why you use RO/DI water. Most people use tap water just fine for freshwater tank. I was wondering if you can use tap water for brackish tanks or not. I am most interested in gobies (specifically bumblebee gobies). Many are sold as freshwater (when they shouldn't be) so, in a freshwater setup they would likely be in tap water anyway... From what I've read, they like harder water anyway (one of the reasons to use RO/DI would be to keep TDS down). Any thoughts on, or more importantly, experience with using tap water with a brackish tank.