simple answer: you were done about two weeks ago. before you add fish, select a disease protocol.
I told this to someone two weeks ago, they added fish with no protocol. one of their clowns is dying and the thread is running as a stuck cycle cause today (everyone debating the .25 api) when in fact they just simply skipped the next clearly described step.
your tank can carry fish two weeks ago, or on day one, bottle bac is this good.
before you add fish now, well after cycling has completed, select a fish disease plan and prep from the stickies in the fish disease forum.
if you choose not to, specifically don't look for the cycle to be the problem if one of the unprepped fish dies/pet store fish are notorious nowadays for this/reason for the advice.
disease is different nowadays, it wasn't like this in 2010. a change has taken place, disease preps are required. try and skirt them if you like

but it wont work. by December... some fish loss would be expected from no prep stocks
that's the trend. within eight months of setup. see the fish disease forum/all the help posts, scan the ages of the tanks asking for crypto brook and uro assistance.
The single most important takeaway you can gain from updated cycling science was that ammonia control happened when you poured the bac out of the bottle, no thought nor coaxing was required. all the thought and prep goes into fish disease preps, that's the new rule which runs massive work