I did a water change today, switching from R/O mix to 100% tap. My GH went up 3 degrees. What I noticed was that the neons in my tank all of a sudden went on a feeding frenzy. Rather than being their timid selves, they were fearless and darting all around the tank. I'm guessing the effect was similar to rain dumping minerals into a lake, and the fish assume that food is on its way.