Water treatment for stout

[Cheshire-cheese]

I've been mulling a recipe over and intend to try a small batch tomorrow as an experiment.
Fermentable Colour Grams
Flaked Barley 0 EBC 130 grams
Mild Ale Malt 6 EBC 1040 grams
Crystal Malt 130 EBC 300 grams
Carafa Special 3 1200 EBC 79 grams

Hops

Cascade 90 mins 8 grams
Northern Brewer 90 mins 8 grams
Golding 15 mins 8 grams


Final Volume: 6 Litres
Original Gravity: 1.055
Final Gravity: 1.016
Alcohol Content: 5% ABV
Total Liquor: 11.2 Litres
Mash Liquor: 3.9 Litres
Mash Efficiency: 75 %
Bitterness: 54.2253183111485 EBU
Colour: 174 EBC

I struggled to use the water treatment calculator with the data from United Utilities' website.
It's years since I made a stout. I seem to recall adding precipitated chalk. Any suggestions.

[Cheshire-cheese]

Hmm I see your point. It's not very soluble is it, something like 0.01g per litre. I suppose the more acidic the solution, the more soluble CaCO3 is, and if the mash is not very acidic, then it's not required.
Is it true that it is less soluble as the temperature increases?
I guess it must be, when I was in France this year, the water was quite chalky and went cloudy as the kettle boiled.