Quick Water Question for tomorrow's brewday

[dammBrewer]

I am trying to use the Bru n Water sheet for calculations. I have done this before and understand it pretty much. However, I have been doing BIAB batches for the last several. The one tomorrow is going to be too big for me to do that; so I need to go back to my 10 gallon igloo and pot combo.

No problem so far. I have my calculations complete on the sheet with 85/15 RO to tap setup as I want it. Question is, since I will be batch sparging in 3 steps after mash; how best do I calculate the 85/15 split? Do I do 85/15 split in the mash water (treated) and again in the sparge water (treated)? Or just do 100% RO treated for mash and then do 85/15 treated for sparge?

Am I overthinking this?

Thanks brothers and sisters in advance....

 

[FirstAidBrewing]

I would do a little digging on HBT, but I looked up a similar question before and I *think* the consensus was that you want your split for the mash as that is when it is more important. The sparge can then be done with all RO

 

[TnkDoc]

I think if you are going to treat the water it wouldn't really matter if it was split.