I've been thinking about why Serenade would help with a Ca lockout. And I came to this possible conclusion:
Since Serenade is packaged as a LIVE culture of B. subtilis, it stands to reason that it is packaged in a medium that is ideal for their survival 'on the shelf'. This very likely includes an agent to buffer pH in the range that they like best, which, since they are a soil bacterium, would be at the same level your plants like in soil.
Just a hunch.