I'm guessing you use straight tap water? You could get a RO unit and remineralize the water to the desired gh/kh. That's what I did and it works great, albeit with a little more work and forethought needed.
Barring that you, you could skip the RO step and add the remineralizer to the tap water to get your desired gh/kh, but I wonder whether that's a great idea because your tap may vary with respect to TDS, gh, and kh over time. So you couldn't reliably add the same amount of remineralizer each time. It would be a moving target. with RO water, you're always starting at 0, so once you figure out the amount needed to hit your target, it's the same every time.