Planted Tank Guru
Join Date: Jun 2012
Location: Gainesville, FL
You have several options to raise your GH.
You can pick up a GH booster at a local store, usually Seachem Equilibrium.
You can make your own. There are several chemicals we can use to raise GH. The most popular being Calcium Sulfate (CaSO4) and Epsom Salt (MgSO4.7H2O). Blend at a 3:1 ratio. Add enough to raise GH 2-3 degrees. Many GH boosters contain Potassium, usually from Potassium Sulfate (K2SO4). This can also be added but may not be necessary dependent on your fertilizing regiment.
Your KH is perfectly fine. In fact, many plants do better with lower KH. I wouldn't bother trying to change this.
CO2 does NOT alter KH. This is a common misunderstanding since it can and does lower PH. CO2 is a weak acid meaning the chemical equation can go right AND left. Only strong acids consume KH. Strong acid equations do not shift left. That's the basic difference between strong acids and weak acids.