Hi ,
I haven't used that. Im sorry. But I am curious why you are using something at all? Is there a reason why you dont use R/O water mixed with a small amount of tap water? Generally many hobbyist will go something like 80% R/o to 20% tap or 90 to 10 if your water is really hard.
If you want to stabilize KH. You could also filter through crushed coral or oyster shells.. ive done that for years to add some kH to my grow out tanks.
-Al