Do you live near a lake with pond scum?

[pinkertd]

:eek3: http://www.boston.com/business/healthcare/articles/2009/09/14/nh_researchers_see_toxin_found_in_pond_scum_as_pos sible_cause_of_als/

[paperdragon]

If it's a toxin produced by cyanobacteria, fishkeepers need to be careful too. I've had cyano outbreaks in my tanks before.