Sounds like BGA, all right.

I had this problem before I got a Python, whenever I let the tank go too long
between water changes. I also sometimes get it when the tank gets too
overgrown, and there's not enough circulation. (Usually growing at the top of
the tank, even floating on the water.) Cutting the plants back so they don't
touch the surface of the water fixes that.


Leigh

http://www.fortunecity.com/lavender/halloween/881/