Quote Originally Posted by Weevil View Post
I think it is algae, the liquid that's made it's waY down the threads and is out of the main circulation and the kill coil can't help down there. Algae killer might help, but if not I would drain the loop and wipe down those threads.
Agreed, but I don't think algae killer will help.

I'd just wipe the threads down with alcohol and put it back together, or just not worry about it.