Tang... White spots on fin

[Metrontech]

What is the acceptable nh3 level?

Or should it be zero always?

[Aquattro]

yes, aim for 0. If you get a reading at all, it's going to get worse by the end of the day. Keep some prime on hand to neutralize it in an emergency. I always keep an aquaclear sponge in my sump so I have a mature filter should I need it for something like this. I've lost more fish to ammonia poisoning than I ever have to disease.