I just used Beersmith and calculated the mash pH, then added lactic acid additions in the mash profile to get to 4.5. Then after completing the mash, I ran it off then added the extra lactic acid. It reduced it to 4.3, so it wasn't exactly the same as adding it to the mash, but it was close. I soured with Omega Labs Lacto blend of Brevis and Plantarum (a 5 day starter) and it went to 2.9 in 16 hours. Really sour.