I thought distilled water has zero everything and a ph of 7..So without alkalinity i can adjust the brewing water with phosphoric to get a ph to 6 and from there take a measurment after i dough in and adjust until my ph is at my target of 5.4..again excuse me im a water noob
Much easier to target your ph before mash and add make your additions. If you're using bru'n water and since your using distilled water, you should be right where it projects. Adjusting during the mash can be done but tricky until you get experience with things. You can lose mash temp quickly, and even over or under adjust PH/ making for a frustrating day.
Edit- you are also seemingly focusing on the ph of your water; that's not what you want to do. You want to know your starting water profile, your grist and its contributions, and your targeted water profile for the beer you are making. Then adding all salts, you will see an estimated PH- that's the important PH value.