Randy - any reply to your question would be pure speculation. First, it isn't known which microbes are in the septic tank product, nor what they primarily feed upon, nor whether they're aerobic or anarobic types - or both, nor if they may negatively impact or possibly depredate upon your pond's naturally occuring desirable microbe population.
One thing is for sure; once you put 'em in - they're there, for better or for worse. Procede with caution, if at all.
Personally, I find it hard to believe that the commercial producers of septic tank microbial products would overlook such large-scale uses for their products IF they were viable pond treatment options.
