Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Seachem or other GH booster for GH. Mostly these are Ca and Mg, but they also have potassium, and some have a few trace minerals. Do not use any GH booster with salt (NaCl)
Potassium bicarbonate for KH.
I am not sure why the RO water has such a high pH, but if letting it sit in a bucket overnight, perhaps with an air bubbler running will fix the problem, that is OK. Add whatever minerals you need to at the same time, and the water will be ready for the aquarium, with the minerals well dissolved.