Finding nitrates

[Proteus]

Not really poking to reduce nitrates just looking to understand where they are comming from. If issue did arise in future I would know the root. I know the tank is new. Just not recently started zeo,
The tank was up running for over a year. Then transferred entirely to my house. The rock bin (rubbermaid) did split while setting up tank leaving rock out of water for a day.

Not really looking for trolls either. Apologies if my terminology isn't up to par. Though I'm sure it's understood :-)