Anything wrong with not adding water salts using RO water in a Cascadian Dark Ale?

[Beer-lord]

My brother wants to brew the W10 Pitch Black CDA by Widmer Brewing. I've never done this one before but he always asks me to put together the recipe and figure out the water additions. When I put the this recipe in Brewfather, the ph is already 5.22 without adding anything at all to RO water. Widmer Brewing's W-10 Pitch Black IPA clone - Brew Your Own
I've never brewed a beer without adding anything. However, when I choose the target in Brewfather as CDA, it drops it down to 5.15 which I'm fearful will make this an acrid beer as it ages.
Suggestions? Maybe add a bit of baking soda to bring it up to 5.35 or so?

 

[McKnuckle]

If it were me I would add CaCl and gypsum in roughly equal amounts to achieve a minimum of 50 ppm Ca. And then I would add baking soda to raise predicted mash pH to 5.4.

 

[JimRausch]

I've read a few posts that suggest that Calcium is not as necessary as we traditionally believe. But..... I'm not sure I believe said posts. I do feel that you need 50ppm Calcium for a good mash. So, similar to Mcknuckle, I would add enough gypsum and CaCl2 to get 50 ppm then balance the pH with either baking soda or pickling lime. I haven't looked at the water formula for a CDA so I can't say what balance of chloride to sulfate I'd use.

 

[Beer-lord]

This is what is suggested in BF for a CDA and I've seen very similar numbers 3 other times in my OCD searching. Can't find much on them anymore.
Thanks for the feedback, I do get a sense that your suggestions are spot on.

 

[JimRausch]

So it looks like approximately 2:1 gypsum to Ca Cl2. I did a CDA from extract back in the old days. Was visiting Burlington Vermont and found the LHBS that Greg Noonan started back once upon a time. Didn't know his name at that point, but the atmosphere from the place was awesome and I just picked a beer to brew out of their notebook. Turned out pretty good. God, I need to get back to Burlington....... Great town.