If it is a matter of alkalinity, it would support Peat's claim that alkaline minerals are interchangeable and keeping an overall high intake matters more. I think Magnesium is more effective if it's of fungal origin, because Calcium can actually promote biofilm formation:
Discovery of Calcium as a Biofilm-Promoting Signal for Vibrio fischeri Reveals New Phenotypes and Underlying Regulatory Complexity. - PubMed - NCBI
Using a calcium chelator limits biofilm formation :
Whereas Magnesium is only anti-bacterial and anti-biofilm, and Mag deficiency is an important enabler of biofilm formation.
Magnesium Limitation Is an Environmental Trigger of the Pseudomonas aeruginosa Biofilm Lifestyle
Discovery of Calcium as a Biofilm-Promoting Signal for Vibrio fischeri Reveals New Phenotypes and Underlying Regulatory Complexity. - PubMed - NCBI
Using a calcium chelator limits biofilm formation :
Calcium Causes Multimerization of the Large Adhesin LapF and Modulates Biofilm Formation by Pseudomonas putidaEGTA also limited biofilm formation in minimal medium with glucose as a carbon source (not shown) and in 1:10 strength LB. This effect of the chelator was compensated for by addition of excess CaCl2
Whereas Magnesium is only anti-bacterial and anti-biofilm, and Mag deficiency is an important enabler of biofilm formation.
Magnesium Limitation Is an Environmental Trigger of the Pseudomonas aeruginosa Biofilm Lifestyle