It is used in hospitals to sanitize (i.e. - kill everything on) surfaces. When I did freshwater planted tanks I wouldn't even use excel. It's a carcinogen (glut. is, that is) - I wouldn't add anything to a tank under my care that I didn't research first - and when I found out what the active ingredient was - forget about it Dave!
There are quite a few threads on planted tank forums about this stuff. Tom Barr did some testing on it, and I was thinking of having a chemist friend with a mass spec run a few tests, but it never ended up happening. Tom will not mention the concentration - I think he's afraid Seachem would come after him if he did, but other aquarists get the exact same results with their freshwater tanks (less fibrous algas in their tanks) by running a generic, known concentration 2.5% solution of glutaraldehyde instead of fluorish excel. I hear it's some pretty toxic stuff at concentrations higher that 5% or so.