Water adjustments in a recipe?

I am confused about how to use the mineral adjustment feature in BeerSmith.  I was looking at the water profile tool and see that you can input the base water volume, pick a target water, calculate adjustments, and save to the target.  What confuses me is how to add water to a recipe.  When I add water to a recipe it puts in the volume for my batch size (I typically use 5.25 gal batch sizes) and the mineral adjustments for 5.25 gal of water.  Is this what I should be adding to the batch?  Should I just add these in the mash?  I was thinking that it would make more sense to mix a large batch of water (10 gal) ahead of time to use during the brew day.  Should I be using the water profile tool for mixing up 10 gal or should I go with the numbers in the recipe formulation?

I don't use the water tool within BS2, but most people that fiddle with water focus on the mash tun to manipulate pH into the desired zone for optimum conversion. 

It's generally easier to do the water math and additions for the MLT since you are already hyper-focused on the water ratio and pounds grist, etc. 

And if you get the pH right there, it generally follows on into the boiler. 

I do separate additions for strike water, sparge water, and boil. I just use the Notes section to track additions. I have no idea what the Water Tool does either.

I manage my water chemistry at a reasonably advanced level: 

• I have mineral additions for the mash to manipulate the pH of the mash. 
• I use a pH meter and lactic acid to make fine adjustments to my mash pH and monitor my sparge pH. 
• I have boil additions that I make to manipulate the flavor profile of the beer and total calcium ions for yeast health. 

I do not make additions for sparge water for two reasons:

[list type=decimal]
[*]Some minerals don't dissolve well in plain water, so they just end up on the floor of the kettle.
[*]It doesn't really do much for sparge pH.  I acidify my sparge water (only), if necessary (generally not) to manage sparge pH. 
[/list]

NOTE: I do NOT attempt to mimic a city profile of any kind.  I have four basic water profiles:

• Hoppy
• Neutral
• Malty
• Pale

These differ mostly in the Chloride/Sulfate ratio.  The pale is special because I build it out of distilled water (my local water has a high RA which doesn't work well for straw colored beer). 

I've used the water profile tool to create water profiles for these various styles of beer.  I have tried to use it to manage my water additions in the recipe (eg, add a volume of a particular profile, and have it compute the additions needed).  I find the tool entirely lacking and makes the process harder, not easier.  Therefore, I now completely ignore its existence and use an external tool to compute the needed additions, and just add those directly to the recipe. 

Plus, there is at least one bug in the water tool that make it less useful for me. 

Tom,  Is there  reason you prefer lactic over phosphoric? 

Not really.  I initially started using it because its consistent with acidulated malt....thus, slightly more traditional.  Now that I have a lifetime supply of the stuff, inertia keeps me from switching.  I know some people like phosphoric, and some claim they can taste the difference.  Since I get close (down to about 5.6) with mineral additions, I'm generally WAAAAY below the flavor threshold in what's required to drop the last 2-3 tenths (1-2 ml of lactic per 5 gal batch).  If I didn't use mineral additions to get close, phosphoric might be an apporpriate choice, since lactic will begin to add a "sour" flavor at higher concentrations. 

I have a 4 oz bottle of lactic 88% that's going on 5 years old and I swear when I used it I can taste it.  I have picked up the same flavor from acidulated too.  Some people are more susceptible I guess or else the mind is playing tricks again.  I got a quart (that's the smallest they sold) of high % phosphoric that I can likely pass on to the next generation unless I use it all for rust conversion. 

Yup.  Gotta do those blind triangle taste tests to be sure.  Here is some interesting work on the topic:

http://braukaiser.com/wiki/index.php?title=Lactate_Taste_Threshold_experiment

For reference, I'm generally at or below an equivalent addition of 1.5% acidulated malt (versus the 8% taste threshold in the above "study").