Add salts to total water or just mash water

I use distilled water to brew and use BIAB. I calculate my water usage assuming 1 gal water added to top up in fermenter (to decrease chance of excessive batch volume). Therefore, my mash water is 1 gallon less than the total water needed by a recipe. I used BeerSmith 3 to make my most recent recipe. I then used the water tab to calculate appropriate salts to add to match a target profile. My issue is that, when I look at the Brew Steps, the Water Prep section shows the full total volume of water (9.05 gal) and the recommended salts. The Mash Steps section, as expected, states only to add 1 gallon less than that (8.05 gal).

So, are the recommended salts to be added to the total volume, 9.05 gal, and then hold back 1 gal for topping up the fermenter (doesn't seem to make sense; why would you add salts at this late point?), or should they be added to the 8.05 gal mash water? If the latter, I want to be sure the program is calculating the appropriate salts for 8.05 gal,and not 9.05 gal.

I would appreciate some guidance.

Thanks.

So if you are using BeerSmith, you would create your equipment profile to reflect the addition of 1 gallon of water as fermenter top-off.  The program would then back that volume out of what is needed for the rest of the process and your mineral and salt additions would be based upon the amount of mash water and not total water.  This way you do not need to worry about splitting your water after treating all of it.

Thanks. That's what I thought, but I just wanted to make sure.

"I calculate my water usage assuming 1 gal water added to top up in fermenter"

You don't want to "assume" anything in Beersmith. As Oginme suggests you need to set up your equipment profile. It needs to be customized to your system and than means taking actual measurements of all your volumes. Here are two tutorial videos that will help...

https://youtu.be/HwEbjOt8OR8

https://youtu.be/QmW7pwQP5mQ

And since you said you are using BIAB here is one for setting up mash profiles...

https://youtu.be/VKiEjhxo2oo

Thank you. That is what I meant. I "assumed" 1 gallon top up water, so I had entered it in my equipment profile. That is what threw me off, actually. Once I did that, I got confused by what I was on the Brew Steps. Fortunately, Oginme explained that BeerSmith is actually calculated the way I would want it to.