I can attest that high levels of humic acid smothers microbes in informal sloppy testing CT Guy and I did. I did try some humic acid (12%) in ACT years ago but did not notice any great benefit so I discontinued. I should revisit some time with some variances.
This could be of interest;
http://www.blackearth.com
This could be of interest;
http://www.blackearth.com