Tank cycled in 2 days?

[MullyJully]

I just set up a 350l tank acouple days ago, new filter, new substrate, plants, everything new. I tested the water today and its show 0 ammonia, 0 nitrite and under 50 nitrates. I was expecting to wait at least a couple weeks.
Has anyone experienced this? Why has it cycled so quick?
Would it be safe to add fish now?

 

[Autumnsky]

It is unheard of that it would cycle completely and be safe for fish with no added filter media or bottled bacteria, because of the nitrification cycle. The beneficial bacteria take weeks to grow into a colony which can process waste. More information will be covered in the article linked below.

https://www.aquariumadvice.com/guide-to-starting-a-freshwater-aquarium/

There are ways to hasten the process with someone's healthy filter pad which already contains the start of a BB colony and also some bacteria in a bottle products.

There is a fishless cycle and a fish-in cycle. Both are linked in the article above and you can decide which way works best for you.