I started getting into all grain brewing about 2 years ago after a couple of years of kit brewing. I collated all of my DIY all grain kit (with heavy inspiration from this site) and completed 4 or 5 all grain brews with varying success. In my quest to make the 'perfect' beer at home, I had just built a fermentation cabinet (fridge, heater and controller) and was looking into water treatment before my free time went completely out of the window and brewing took a back seat. Why you ask - kids! We've now got 2 young children so brew-time is very hard to find and I've not yet tested my fermentation cabinet or treated my brewing liquor

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So, to the point. For all grain, I was going to use the brupacks guide to water treatment as my basis for water treatment. I live in a VERY hard water area (Cambridgeshire) and suspected that my all grain efforts were tainted by my 'hard' liquor. I do not have the time to try and understand the full chemistry behind perfecting the liquor so the brupacks approach sounds like it will suit me fine (campden tablet followed by testing with a salifert kit and adjusting with CRS and DLS). I think I understand the principal for all grain brewing (i.e. adjusting the liquor to match the profile for the intended beer style) however, how does this translate to kit brewing? What water treatment is needed for kit brewing on the basis that there is no mash to target ph levels at? I'm concerned that my hard water was/will also affect my kit brewing as I was never completely satisfied with my kits hence moving to all grain. I've search for topics on the subject but couldn't find anything.
All help and advise much appreciated (as long as it is simple!)

Thanks!
Dave