Well you can can add an off the shelf buffer such as Kent super buffer (dissolve in di/ro water first) or the alkalinity part (part 1 I think) of B-ionic if your using that. I like to keep my alkalinity around 10 DKH.

Some might say just use baking soda but I like to use a balanced buffer (carbonates & bicarbonates). You can make your own with baking soda and I think washing soda. I'm sure GaryP can give you the recipe.

BTW, are you using two seperate test kits to measure alkalinity(meq/l) and one for KH(dKH)? If so, it really isn't necessary since they are the exact same thing. (meq/l * 2.8 = dKH)