dKH - make up water

[aaronc]

Hi,

I am trying to match the parameters of my make up water to the parameters of my tank before doing a water change. I am using Ken Pro Buffer dKH. I do a 20 gallon water change but mix 10 gallons in 2 containers. The make up water after adding only salt has a dKH of 6.16 and I would like to increase it to 11 dKH. The instrution on the bottle say not to exceed 1/2 ml per gallon in a 12 hour period. I assume those instruction are for adding directly to the tank and that it would be safe to add more @ one time to the make up water. How much buffer would I need to raise my dKH from 6.16 to 11 dKH? Can I add it all at once?

Thank you,

Aaron