I have what has to be the softest well water in recorded history-- GH around 50 (color is between the 40 and 80 readings so I'm guessing); KH less than 80--as well as ridiculously low pH at 6.2 or thereabouts. Apparently when they said RCS liked "soft and slightly acidic" water they did not mean THIS soft or THIS acidic.
That's moderately soft and only somewhat acid; some of the natural environments of our fish are in the low 5s and only trace GH and KH. I wish I had water like that; ideal for most of our fish.
What are "RCS"? I can't keep track of all these abbreviations people use.