I've been thinking about this water stuff as well. Looking at the Ward lab results in the BYO article a couple of pages ago, Michael's beer was pretty consistent with Heady Topper except for the SO4/Cl ratio. I mean, across the board, including Ca, Mg, Na and K. If you compare that to the Alter Ego results, Michael's SO4/Cl is pretty close, but the Ca is way low on Alter Ego and the K is way high. Sorry that this is just stating the obvious so far. But I feel like KCl is a pretty elegant solution to this. It would keep the Ca low and put Cl and K in the ballpark. The other possibility is that TH is using some combination of malts to get there, but the K is so much higher and Ca so much lower for the same SO4 + Cl than Heady or Michael's beer that I feel like KCl is more likely.
So... I added KCl to the spreadsheet I use for my water adjustment. I'm not necessarily trying to match the specific numbers from Alter Ego, being that a lot goes on between brewing liquor and finished beer. But I feel like it's safe to say TH's adjusted brewing water is most likely high Cl, some SO4, relatively soft with some alkalinity.
So my local water profile is:
Ca 25 ppm
Mg 8 ppm
Na 5 ppm
Cl 11 ppm
SO4 23 ppm
HCO3 96 ppm
K 0 ppm
If I cut to 3/8 distilled, I get:
Ca 16 ppm
Mg 5 ppm
Na 3 ppm
Cl 7 ppm
SO4 15 ppm
HCO3 60 ppm
K 0 ppm
For 5 gal of strike water, if I add 2.8 g of CaSO4-2H2O and 7.5 g of KCl, I get:
Ca 50 ppm
Mg 5 ppm
Na 3 ppm
Cl 195 ppm
SO4 97 ppm
HCO3 60 ppm
K 208 ppm
I think this is the profile I'm going to try to hit for my next attempt. About 200 ppm Cl with a 2:1 Cl:SO4 with 50 ppm Ca, some of which will precipitate out. Not worried about the K because a lot comes with the malt anyway. Hopefully this will get me close. I collect mash/strike and sparge water separately and will adjust both to the same profile. Brewday isn't until Dec. 2nd though. Pre-negotiated with SWMBO haha.