What is this black stuff in my new circuit(its not algea)

I can not figure out what this black stuff is in my circuit. I just noticed it. It has been closed for 24 hours and has run for about an hour. Just curious if anyone know what it is. The water is distilled. No treatment has been added. What amazes me is how small the black stuff must be to get in the threads of the res. I dont notice it anywhere else in the system. I guess it could be something from a rad or the pump. Any ideas?

Could be paint ?

since you just got a new bix2 radiator, its the paint in the radiator. you should flush out the rad before you run it in your system.

yea he prob right

cool thanx, ill do that