Yes, I had some tetras and GBR's die when I accidently overdosed. I had done a plant dip, and then put some of the dip solution in the tank, and I guess it was too much. Within 5 minutes, the fish were surfacing.
55G Filstar XP3 - 16" Fire Eel
75G Medium Planted - Filstar XP3 Low Light - Established Feb 2006