So why wouldnt you get the strike water around 5.4?
'
Because the buffering capacity (the measure of a substances resistance to change in pH via the addition of acid or base) of the grist
dwarfs the buffering capacity of pure (de-ionized, or DI) water. That means a small amount of added acid or base will alter the pH of
"pure" water to a very high degree, while at the same time altering the pH of the recipes mashed grist (its aggregate of component malts, unmalted grains, and adjuncts) to a very low degree (relative to pure water).
The presence of the ions of certain minerals (primarily Ca++ and Mg++) and/or alkalinity (mainly calcium and magnesium bicarbonate, which are both conflated into and then quantified in units of CaCO3) in water alter its capacity to pH buffer, with this alteration ranging from close to none at all, and upward to a small amount, or upward to a large amount, and lastly to a very large amount, based upon their respective quantities, and this is why
you truly need to have a firm grasp of their quantitative values via an analysis of your water.
Darker malts generally have DI water mash pH's below 5.4 (down to about pH 4.2 in some cases), while lighter colored malts (be they barley or wheat) have DI water mash pH's that are above pH 5.4, and can be found to be as high as roughly about pH 6.1 in some cases. Light colored malts form the basis (make up the predominant part) of nigh on all beer recipes, and are thus called 'base' malts (though ironically, for those who speak English at least, they could just as well have been given this designation due to their pH characteristic). A ballpark rule of thumb is that the darker the malts color the more relatively acidic it is with respect to the alpha and beta amylase enzymes peak activity midpoint of pH 5.4 (as opposed to being rated as acidic or basic with respect to pH 7 as most who do not understand brewing requirements would likely first expect).
In brewing, malts with a DI water mash pH of above 5.4 are considered basic. The degree of a malts classification as to being basic or neutral or acidic is further determined by its categorical classification, as in: base, specialty, caramel, crystal, deep roasted, etc...
A subject that continues to be ignored here is: Does NYC treat its water with flavor damaging chlorine and/or chloramines?