Could this honestly be algae? (Now with pics..)

[millertime359]

That is the only place then? It could be algae as someone already stated, there is not circulation down there, so the silver isn't really going to help. If that is the only place, I would just let it be, then tear your loop down later. You could put some silicon on the threads to keep water from getting in there after you clean it.

Algae killer is just a couple drops of liquid that will at least keep the active flow of the loop free of algae. Probably a good investment to make so it doesn't spread to areas like your blocks and lower flow areas.

Seeing he has silver and the Primochill tubing, don't think he needs to add any PT Nuke too.