Mine did the exact same thing. Get some dr tims one and only and ammonia in a bottle, that should work
If there are already fish in the tank, I wouldn't add any ammonia to the tank.
If you have had live rock and fish in the tank for 3 weeks with no ammonia or nitrite spike, you are fine. The live rock had enough bacteria and your tank is cycled.
I would wait a few more weeks before adding anything else though.
Oh, by the way, welcome to R2R!


