I usually dont post on THIS site but I was doing some research and came across this poll and HAD to put my 2cents in.
Make no mistake if you are using tap water you are rolling the dice with your tank!!
Even in places with "good water", such as where I live, it is still filled with minerals, metals, chlorine, etc. conditioners dont work as good as you might hope.
In a small enviroment such as a tank those elements will eventually reach unbalanced levels.
Also municipal water treatment and delivery systems have a high rate of fluctuation due to thier nature. Some so much they have to issue BOIL ORDERS once in a while when the levels get to high.( even in Chicagoland)
TEST, TEST, TEST and you will learn as we all haved.
I dont mean to sound like Im bitching, Ive just been there done that.