Thanks guys for your input. It is in line with what I was thinking. When I do the mix at w/c, overall the water is at 3kH, 5gH. The only thing I was thinking/trying to reduce was gH, to about 3, same as kH. I thought that maybe r/o+di vs. r/o would play a role in here. It seems to me that with r/o mix to tap water, I can reduce kH much faster, but gH seems to resist and stays at around 5 as Tom had suggested.