Now I know Dr Hovanec cultures and sells One and Only Baottled bacteria, but he also participated in the major research which identificed the most likely bacteria doing the work in tanks, especially FW tanks. Here is a quote from his site about when to use his product:
When should I use One & Only?
Use One & Only when setting up a new tank and after major environmental changes to your aquarium. Examples of major changes include a disease treatment with antibiotics or chemicals that are harmful to the nitrifying bacteria, after a major gravel cleaning which can disturb the bacteria on the gravel and after a failure of the filter.
from
http/www.drtimsaquatics.com/resources/helpful-hints/one-and-only-nitrifying-bacteria-faqs
In the research bacteria was collected from the gravel in one and from gravel, filter material and even water to identify and/or culture it from. Bear in mind the bacteria cannot tell a filter from a rock in terms of it being a good place to live, the bacteria attach to hard surface and multiply best where there is a constant supply of what they need. So anywhere there is good circulation and shelter from light they will thrive.
In most tanks filter media is usually disturbed much more often than substrate is over turned, which favors the presence of bacteria on the gravel and decor. Substandard filter maintenance also would favor this even more strongly.
All of this is not to say that filter media is not the best place to find high concentration of bacteria, but it is a mistake to assume this means what is on the substrate is not significant. Big vacuumings cause ammonia spikes for two reasons- the good bacteria loses its oxygen source when it is turned over and goes deeper, and that turns them off and eventually kills them. And then there is all the gunk stirred up.
Move the tank and the gravel (kept damp). When you get there fill the tank with dechlored water at proper temp and then run your filter(s) with a bunch of floss to clear up the water if its dirty. The fish will be fine in the bags for another hour
. After all shipped fish travel in bags for days between where they were born and when they arrive in our tanks. No big loss of bacteria, no dirty water or serious ammonia issues. Change out or remove the dirty floss and add the fish.
Of course the above is just one fish keepers take on things.