Other the fact that you are not accounting for the 1ml dilution from the adjusting solution, your math checks out.
Yeah, I know. I figured it was a pretty good approximation to get some club members excited/informed about the possibilities of water adjustment. I can deal with a 3.5% in this setting.
I don't think in math this early, but I'd sure love to be a part of that talk, sounds great!
My club has started keeping the PDFs of our presentations (some have audio recordings) here if people are interested in listening to myself and other club members talking about nerdy stuff. This presentation will be up probably by the end of the month.