The beneficial bacteria adhere to surfaces in the tank (mainly the filter media in a newer tank; as the tank matures, the BB will colonize on all hard surfaces within the tank), so there's no danger in losing BB when vacuuming the substrate.Great! I’m using a siphon and a couple of 25 litre Jerry cans. I’m not vacing the gravel as assume this will suck up what bacteria is sitting on the substrate?
If using vessels to refill the tank (not sure what a "jerry can" is, lol), then use enough Prime to treat the vessel amount only; if using a hose to refill the tank, use enough conditioner to treat the entire tank volume.