Should I add CaCl2 to mash, sparge or both?

I just received my water report from Ward Labs, and I think I have identified what may be giving a harsh bittering in my darker beers....I'm guessing at least part of the reason may be due to the high sulfate concentration....especially in proportion to the chloride level. If anyone thinks otherwise, I'm all ears as I'm just getting started with these water adjustments!

Sodium, Na 60
Potassium, K 6
Calcium, Ca 36
Magnesium, Mg 19
Total Hardness, CaCO3 169
Nitrate, NO3-N 0.8
Sulfate, SO4-S 70 (converting it to SO4 brings it to 210)
Chloride, Cl 21
Carbonate, CO3 12
Bicarbonate, HCO3 60
Total Alkalinity, CaCO3 69

Anyway, without diluting to get the sulfates down, it looks like if I add some calcium chloride it will help balance things out a bit. Also, looks like I could do with some added calcium anyway. I'm hoping that by adding some CaCl2 it will make for a good overall balanced water profile.

Yes, the chloride (once adjusted with CaCl2) and sulfates will be a bit on the high side (although within an "acceptable" range)....please let me know if you think they are approaching "warning" levels and if I would be better served to dilute anyway.

So assuming I plan to go the CaCl2 route, what is the prevailing opinion on adding it to the mash/sparge? Should I add all of it to the mash or split it up in proportion to the total water volume? Or perhaps even add it to the boil? Does it matter that much one way or the other? Or am I going about it all wrong and maybe need to rethink my strategy?

Adding CaCl2 won't "erase" the sulfate level. I'd dilute at least 50% with RO water (to reduce the sodium and the sulfate level) and then add CaCl2 to get the calcium back to 50 ppm or so.

+1 to Yooper's comments. You can't add ions to reduce the effect of another excessive ion. Although 210 ppm sulfate is not bad for a hoppy pale ale, it may clash a bit with roastiness in dark beers. I note that no historic porter or stout brewing city has sulfate concentration that high. Dropping the sulfate to 1/2 or 1/4 of the original concentration appears appropriate.

Thanks Yooper and Martin! That specifically addressed one of my concerns, which was the potential of the added chloride to in effect "cancel out" the excess sulfate. Per your recommendation, for darker beers I will try diluting with RO and see how that works out.

So if I was to cut with RO and add some CaCl2, would you recommend adding to the mash and/or sparge?

I recommend adding most minerals to both the mash and sparge water. Only alkalinity producers like baking soda and lime are not added to the sparging water.

Thanks, Martin...I'll do just that!