Wanted to post an update on the IPA that was the first batch I did RO + salts for.
It's a crazy success! It was my second time brewing this recipe (EdWort's Bee Cave IPA), and it was certainly good the first time. Tasting notes for the first batch really came down to wishing that it was a trifle less sweet/malty, and a trifle "better rounded" when it came to the hop impression.
Using customized water, the hops have become much better balanced and yet more forward (which is dynamite for this IPA), and the malt was indeed more subdued. One effect I wasn't expecting was that the beer has much better mouthfeel this time around, and seemed to clarify more completely after less time.
I was a bit worried that having used chalk in the sparge water I might have had some high-pH tannin extraction, but if that happened, it's either become part of the hop character I like, or was so subtle that it hasn't impacted the beer in any negative way.
For those interested, my method is this:
* grab the ion profile I want for the recipe in question from Bru'n Water and put it into BeerSmith as a water profile
* open up BeerSmith's water profile tool and set the source water to RO and target to the Bru'n Water profile
* auto-generate the salt additions for the mash water volume and save it to a new water profile
* auto-generate the salt additions for the sparge water volume, then zero any baking soda or chalk amounts to avoid any pH problems, and again save it to a new water profile
* add the new mash and sparge water profiles to my recipe, checking that the volumes are what the recipe's mash and sparge call for, and match the volumes used to calculate the salts
I know this doesn't do any compensating for the lost baking soda or chalk, but this method is simple and reproducible enough that I'm happy doing it as each recipe requires. So far the results have been excellent.