Malticulous I think you're right, thanks for the link. I've read Kai's work on Understanding Efficiency, but I never read his work on Understanding Mash pH.
Link to Kai's work on Understanding Mash pH
I always assumed my mash was falling into the acceptable pH range 5.2-5.7, and that was good enough. I think on this last batch, I finally pushed the mash into the desirable or optimal pH range 5.3-5.5, and that is what made the difference.
After reading Kai's work on Understanding Mash pH, I can see that mash thickness plays a big role in pH. Which is very important for enzyme activity. With a thin mash 2.4 qt/lb(5 l/kg) the malts alone can't push the pH low enough into the optimal range with an average recipe of 85% base malts, and 15% cara malts.
The more water in the thinner mash, the more its pushing the pH higher against the malts trying to push the pH lower. Keeping the pH above the optimal range.
The less water in a thicker mash, the less its pushing the pH higher against the malts trying to push pH lower. Allowing the pH to drop into the optimal range.
Here's my best interpretation of what happened after reading Kai's work. When I added the Calcium Chloride the Calcium reacted with the phosphates in the malts to form Calcium Phosphate which dropped out of the mash leaving free Hydrogen ions H+ to push the pH lower than the malts could do alone. I'm going to repeat the same recipe next batch to see if I get the same results.
Here's a few charts from Kai's web page that really show the differences in mash thicknesses effects on pH. In the first 4 graphs the highligted boxes show random generated mashes from 10-20 SRM made of 85% base malts, and 15% cara malts. In the 1 qt/lb mashes the malts were able to push the distilled water pH down to a level of 5-5.33, but in the 2.4 qt/lb mashes the malts were only able to push the distilled water pH down to a level of 5.33-5.48. If these mashes were typical brewing water and not distilled, the brewing water would push the pH levels even higher. So from Kai's work, I think it's safe to say that even though pH levels are important in any mash, in a thinner mash like a full volume mash they're even more important, since the mash has more water, that water has more effect on the pH. Thanks Kai for doing all the hard work.
This second graph shows pH levels of distilled water with 210 random generated mashes at a mash thickness of 1.4 qt/lb(3 l/kg).
Link to Kai's full work partly shown here