Those store-bought additives such as Fritz-zyme and Stress-zyme contain these bacteria in a suspended state, if you are looking to add some. Just as David said, all these bacteria need to increase their #'s is sufficient surface area to physically hold their colonies, and suitable waste to keep them alive once established. If you are having problems in your system with elevated ammonia or nitrite, I would add more LR (surface area) rather than adding additional bacteria.
These bacteria are ubiquitous (found all around) and will seed any submerged item quickly if the water surface is exposed to the outside air. I think that most people do not advocate buying these additives as nature will provide in 2 weeks what we pay 7.95$ to pour in.
