Why all the hating on the chalk? I've only used it a couple times when trying to match a particular brewing city's water profile.
Because it doesn’t dissolve well in water, without extraneous measures like bubbling c02 through the water, so just falls out as precipitate anyway. Which is probably a good thing in your case, because if it did dissolve, it would likely raise the mash pH too much if you were trying to hit a city’s water profile.
Brewers don’t often use the water from the city without boiling it first, for example, to precipitate out the chalk. So that might make the “profile” but not the brewing water that was actually used. Generally, alkalinity is rarely desirable in brewing water unless making a porter or stout.