there are no algae in a closed circut.
1. what on earth should they feed from? every life form needs sth to eat.
2. algae would require light.
Are you just pullin my leg?

Algae is a very common problem here in the states. It gets light from the room lighting, LED's, and flourescent lights everybody seems to put in them these days. If I don't add an algacide to my Koolance Exos every few months I get brown stuff growing in the tubes. I start out with distilled H20 and add some stuff like anti-freeze, but the stuff still grows unless I add an aquarium algacide. :'(