Ugg I agree cycling stuff is confusing there is a mix of sales and science, the two not always agreeing
the context for those two options above is that both will feed the bacteria one might add with bottled bacteria. So would a pinch of fish food as it breaks down into ammonia, all the same ends. The added bottle bac are so hungry for ammonia they don’t let it build up, so fish added wont die in their own waste if someone chose that route.
Today’s best fish disease control involves waiting nearly three months to add fish, in an approach called fallow tank prep
months without fish to attach to / feed on / kills off most known disease agents. The aquarist at the right time would add healthy fish with no disease (they were quarantined) and that approach means the fish are best prepped.
fish-in cycling works, feeds bacteria so they can multiply, but it skips fallow prep and the fish added for ammonia production also immediately seed the tank with disease agents which feed on those fish, they’re never starved in fallow prep
**i have ran online cycle threads where we did actually opt for two clowns at the start, we skipped fallow. The rationale was, clowns are mass produced nowadays and every nano on the planet has some, they’re rather tough, and the aquarist didn’t want a big mix of fish they wanted two clowns in a 30 g nano so we did, and they’re fine. They have a disease risk but it’s low, whereas the reefs you see with mixed fish certainly wouldn’t be ok mixing different strength fish in a soup of non fallow water. most people want more than just clownfish, so we advocate the fallow approach for typical reef tanks.