"Wm Hopkins" wrote in message
ink.net...
I've had my tank up and running for 2+ years and in the last month an odd
(for me) algae has started. It grows in small circles and is bright green.
Never higher than 6" from top of tank and hard as all get-out to clean
off -
usually requires a razor blade. Very slow growing. Lighting is 2x55W CF
5300K over a 110 African tank. Nitrate is ~10 Ammonia and Trite are
undetectable. Any ideas?

http://faq.thekrib.com/algae.html#spot

I have it too, AFAIK, it's something you just have to live with.