Lots of discussion about that stuff ... not sure if there's a conclusive
answer. Check out:

http://fins.actwin.com/aquatic-plant.../msg00014.html

"paul" wrote in message
m...
Hi, I am using the Hagen CO2 system for about 1 week. Then I find that
there are some white fuzzy stuff appear around the end of the tube in
the water. This stuff is developed inside the diffuser. I tried to
clean it up but it shows up again in the next day. Is this stuff
harmful or not ? Any experience about it ? Many thanks.