There is a difference in bacteria for septic systems and bacteria for ponds. Basically, different strains are used in septic products to address the waste found in septic tanks. For instance, you need bacteria that can readily feed on human waste, oil and grease and produce the associated enzymes to break that stuff down. Same thing goes for ponds, there is different types of waste in ponds, so you will want a slightly different bacteria bend to better address pond waste. This is not to say that they two products are totally different as most will share the same strains, but there will (or should) be some difference.
I will also say that I would not pay too much attention to the claims of 20-30 species of bacteria in a products as many time those "additional" species really dont do anything. From what I have seen there are maybe 6-8 or so good strains for pond bacteria
