I'm not sure the problem with tap water has anything to do with the bacteria, it's more about what other minerals are in the water, like phosphates and silicates that feed algae and diatoms. I had diatoms pretty bad at first (I filled with tap), and they didn't go away until after several months of regular water changes and some Seagel. It wasn't that big of a deal, just an aggravation. However, I have well water, not city water, so I don't know if that feeds into it or not. Just something to think about.