Dark Beer with Seattle water pH problems

I live in Seattle where there is relatively neutral water.
Ca ppm = 26.2
Mg ppm = .37
Total Hardness CaCO3= 67
Alkalinity= 18.9

I used Palmer's nomograph to flesh this whole thing out and it basically tells me I'm brewing with 5.7 pH water. I'm going to try to brew a dark oatmeal stout this weekend (SRM ~25-30) and using the nomograph I calculated I'd need about 180 ppm bicarbonates to get my RA into the right range (6.0). Palmer wrote you might want to split up your salt additions between chalk and baking soda. Long story short:

I came up with about 10 tsp chalk (145 ppm) and 9 tsp baking soda (35 ppm) in a 4 gallon mash to get my pH after the addition of dark grains up to 6.0. This will be my first go at a darker style beer and in my very un-educated opinion that seems like a lot of salt addition... am I wrong or should I go ahead with these additions?

Don't do it! I live in Seattle as well and just ruined a batch of stout doing the same thing. While Palmer's nomagraph seems to work for medium bodied/light beers, when it comes to stouts, etc, it seems to overcompensate way too much (in my experience at least), suggesting you need to add huge amounts of alkalinity. Using his formula verbatim, my mash ph ended up at about 6. The resulting beer was so acrid I had to dump it out.

What does everyone else think? Has anyone else had this problem?

Isn't the target pH for a dark stout in the 6 neighborhood though? I wonder if there's some oversight in the mineral profile of the water here that we're looking past... Cl maybe?

I'm no expert on water chemistry, but I'd just like to chime in and say that I brewed a porter on ordinary Seattle tap water a few weeks ago. I happen to be drinking a glass currently, and I think this is one of the best porters I've ever had. Take that for what it's worth.

I would consider a ph of 6 to be pretty high...Wouldn't you want to end up with a target mash ph of 5.2 regardless of style?

I'm definitely not an expert in the area...but from what I got out of "How to Brew" by Palmer, the darker grains impart acidity that will lower the pH of the mash. The overall target of the mash is going to be in the 5.2 range, but to compensate for the acidity in the grains I think you want to add the bicarbonates. Then again...I could be turned 180 degrees the wrong way.

Something to consider: http://www.fivestarchemicals.com/tech/fivetwo.pdf

I'm nervous to use that 5.2 stuff. Is there anyone who is prepared to swear by it, or should I just turn my palms skyward and use the Seattle tap?

10 tsp is alot. Are you sure you converted the grams correctly? You should adjust the water, especially for stouts. I'm away from my notes but just use -TH-'s EZ water. Do a search for it. It's much simpler an more user friendly than palmer's. Also, when you add additions to the mash you can add baking soda, but leave it out of the kettle because you already mashed to get the proper pH and the baking soda will also add sodium, which you don't want in excess.

I think your water is like this... and what additions PER GALLON I'd make.

Starting Water (ppm):
Ca: 17
Mg: 1
Na: 4
Cl: 4
SO4: 2
HCO3: 18

Mash / Sparge Vol (gal): 1 / 1
Dilution Rate: 0%

Adjustments (grams) Mash / Boil Kettle:
CaCO3: 0.5 / 0
CaSO4: 0.5 / 0
CaCl2: 1 / 0
MgSO4: 1 / 0
NaHCO3: 1.5 / 0


Mash Water / Total water (ppm):
Ca: 172 / 94
Mg: 26 / 13
Na: 112 / 58
Cl: 131 / 68
SO4: 179 / 90
CaCO3: 315 / 165

RA (mash only): 178 (20 to 25 SRM)
Cl to SO4 (total water): 0.75 (Bitter)