Black fungus?
 

Can anyone identify this 'stuff', whatever it is. It's taken over the top of this moss, but it's isolated so far to this single pot. Dont know what it is, just need to know if I should do more than a quick repot and physan treatment. Thoughts?

It could be dead or otherwise blackened algae rather than fungus
Hopefully others can chime in with their thoughts and advice1

Hard to tell from the picture, but it looks like mold. If it is, the Physan and repotting should take care of it. Allow to dry a little more between waterings and make sure you have good air circulation. Oh, and make sure you don't leave old sandwiches around your growing area :)