As demonstrated in the various products in the following link, the Bacillus genus is the main bacteria family used in septic tank formulas.
http://www.bio-cat.com/products
It is also the main *probiotic* bacteria family used in aquaculture formulas, including probiotic fish food formulas.
With regards to growth performance, immune response, or out-competing pathogenic bacteria via competitive exclusion, as stated previously the science is still in its infancy - and could be highly subjective to species, as well as the growth stage of species, etc-etc.
That leaves us with improving water quality (by increased waste reduction), which again places the bacillus genus of probiotic bacteria as #1. So while one may never be privy to the proprietary information regarding most of these various septic tank products, it's safe to say that the vast majority of them will all be based on the Bacillus genus of *probiotic* bacteria, with a few in-house tweaks & twists with some of the various septic cleaner brands.
The main thing is using a product that is 100% organic, biodegradable, and non-toxic. That doesn't mean that you should feed it to your dog, or dump the contents of 10 packages into a 5 gallon tank full of guppies.
KingofKings ............... I find it difficult to entertain comments from naysayers that are basing their negative conclusions on nothing more than speculation. It also seemed quite clear to me that the poster did not understand that heterotrophic bacteria can be gram-positive (eg. Bacillus) or gram-negative (eg. Pseudomonas), and while some are designed for anaerobic conditions, some are strictly aerobic, while many are facultative anaerobes, which means that they can survive in both the presence or absence of oxygen.
I cannot prove one way or the other what (if any) effect the product that I use (SeptoBac) has had on the growth or overall immunity of any of my fish, or whether it is out-competing pathogenic bacteria (hopefully I don't have any present in numbers that could be problematic) - but what I can say with 100% certainty is that the *probiotic* septic tank bacteria I have been using for the past several months has most definitely reduced the organics in my tanks, and filters. That alone has been well worth it for me.
The only difference between what I'm using, and what is sold in pet stores across America, is the product that I'm using costs a tiny fraction in comparison.