Al,
I agree with you. I think the potential addition of the excel is secondary to an already exsisting bacterial infection in the discus. This lesion i have seen too many times in discus. It is always the same. Looks very much like a heater burn with white fungus look to it. It took me 9 months of intensive reseach and the loss of 1 discus and 1 angelfish as well as information gathering from many other people to get an absolute answer to what caused it.
I would be more than happy to share this information with the forum. It will take a while for me to write it up but i can do so.
Tammy