Hi bs6749, thanks for responding. Let me explain my situation...I just filled my 75 gallon with a split of R.O. and tap. If I am reading my GH and KH test kits properly, then 1 drop = 1 degree of hardness. Therefore, my tap has about 7-8 degrees GH, 7 degrees KH, and a PH of 7.2-7.4 straight out of the tap, and higher when it has sat out. Not that my water is hard necessarily, but my goal is a pH of 6.8, which my tap does not have. I have been experimenting with mixing tap with my new R.O. unit, but I am uncertain where I should keep my GH/KH levels at, and it's driving me crazy. If I keep my KH at that 4-5 range, then my pH goes above 7.0. I can go into this further, but see what you think about what I've said so far. Thanks!