[iggiebee]

Maybe a little late for this, but it's good advice:

Make sure when you FIRST assemble your WC rig, to make a first run with your favorite cleaning agents... Why? to remove the manufacturing extrusion oils from the tubes, and/or soldering resin residues from the radiator of course.

That whitish-creamy-powdery thing that may appear in tube's walls after a few hours days, most probably are these organic compounds decomposing and not any algae or bacterial growth at all. So you thought you had only pure ditilled water in your WC system.

What these decomposed organics will do for sure, is provide the nutrients for future healthy algae/bacterial growth.