[QUOTE=Straight shooter;8876586]Seachem equilibrium is a blend of magnesium sulfate, calcium sulfate, potassium sulfate, iron sulfate, and manganese sulfate - hard water elements plus iron. This is enough to set GH levels wherever you desire.
It doesn't contain carbonates so won't affect KH. You can use Seachem Alkaline Buffer for this, or baking soda etc. Carbonates buffer pH, other hard water elements only tend to buffer a little. You'll need to use measurements of KH (we test this in home aquaria using alkalinity) to set pH levels.
This has been my experience. I do water changes with RO and the result is very soft(1 or less KH, 2 or less GH) and very low PH(I usually get a reading of 6, the lowest range my test kit will measure so it could actually be lower) unless I condition the water. The Equilibrium gets the GH up in the 3-4 range and I use baking soda and Seachem Alkaline Buffer(mainly because I have it on hand) in egual parts to raise the PH enough that I know my reading is at least the 6 my kit measures or a little higher.
I use TDS readings mainly to monitor change, not as a GH indicator.