"Craig Brye" wrote in message
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Does anyone have any ideas on what this might be?


Commonly called "green slime algae", it's not even really an algae at all,
it's a cyanobacteria.
Read about it he http://faq.thekrib.com/algae.html

I have had it a couple times, and treated with erythromycin. Went away
within days. Some, as the FAQ suggests, feel that the medicine may damage
the bio-filter bacteria, but my tanks did not experience this. YMMV, always
use care when administering chems and drugs to your tanks.