I'd cut off any light source - period - for 48 hours and see if the color changes to brown. If it does, take your case out of any natural sunlight for awhile.

Don't really see any need for adding chemicals you probably don't need.

Algae usually starts off as a film - before it get's hairy as you mentioned, and this does look like a small algae bloom from your photos.

It wouldn't hurt to take a real close look at your loop for small dark spots...it could be signs of a larger problem.

Best,

Liquid Cool