Advice on controlling mash ph with step infusion mash schedule

[demetman]

Hello, I have been recently exploring classic and historical recipes, which would require or greatly benefit from step mashing continental, wheat and under modified grains. I brew all grain, 5 gal batches. I mash in a 10 gal igloo cooler and batch sparge with 1 step. All recipes a formulated with beersmith and I use bru'n water for salt additions to create a water profile appropriate to style and controll mash ph from 100% RO water.

I'll use my last brew day as an example of my process and the obstacles I'm facing.
Grodziskie 5.5 gal efficiency 84% OG 1.038 IBU 34.6 SRM 3
7# Oak smoked wheat malt
1# Rice hulls
3oz Acid malt
3 step infusion mash
7.80 Qrt water @ 107.1 for 100.4 30 min rest
2.85 Qrt water @ boil for 125.6 40 min rest
9.30 Qrt water @ boil for 161.6 30b min rest
Ph at 15 min after mash in was 5.24 @ 67.8F. I added 1.33g CaCl2 at dough in.
Ph at 15 min after 2nd infusion was 5.42 @ 71F
ph at 15 min after 3rd infusion was 5.6 @ 75F. At this time I added 1oz acid malt to try to reduce mash ph. Mash ph 5.51 @ 71F. I then added 5 drops 88% lactic acid to try to reduce ph further. Ph was 5.49 @ 68F by then end of the mash rest. After vourlof, I batch sparge with the remaining 2.5gal water.

Is there a way to better control mash ph? It is quite taxing to try to adjust mash ph after subsequent infusions that barely allow mash ph to stabelize within the rest time. I encountered the same situation with a previous batch. I appreciate your thoughts and recomendations

 

[helibrewer]

You could adjust your boil water additions to pH 6 or proportionately split your salt additions between all water additions.

 

[demetman]

I use Members Mark purified water from Sam's club. Right now the ph of that water is 6.10 at room temp. Would that .10 make a difference for buffering mash ph? I sort of split my salt additions for the last batch. I added as much salts as needed 1.33g calcium chloride to mash water to target low end of ideal ph range(5.2). The remaining salts, 2.14g calcium chloride went into the water for all other infusions, including mashout. When step infusion mashing, is it a common issue of controlling mash ph?