How to tell if a tank cycled?

[Ghostyboythedog]

Hi,
I have a 20 gallon saltwater tank and I've had watering it for 4 days how can I tell that it's cycled and ready for fish?

 

[Ghostyboythedog]

Hi,
I have a 20 gallon saltwater tank and I've had watering it for 4 days how can I tell that it's cycled and ready for fish?

Water in it*

 

[Mr. Mojo Rising]

the ammonia would be zero and you would have some measurable nitrates. That’s when the cycle is done.

Are you testing? How did you start the cycle?