Brown layer in reservoir

[oerekum]

What kind of "anti-algae" did you use?
We both have thermochills, perhaps it is just flux then.

Sorry I missed your post. Seeing as this residue is white I think it is indeed Thermochill residue, other posts on these forums also say it looks like it. It's the only place in my loop where I found this residue though. I brushed it off with a toothbrush that's been demoted to computer cleaning, and some dish washing soap.