The UV portion of sunlight ought to kill bacterias, if the UV is strong enough. The rest of the spectrum of sunlight would, indeed, promote algae growth. Hence the UV sterilizer thread
I still haven't experimented with Water Wetter, but i'd certainly like to see this slimy deposit that it's alleged to leave.
I like to have clear tubes because I like to see what's going on. I could use black rubber tubing, but that's actually harder to find at the hardware store... go figure!