I have never used Esha 2000 on Discus (yet), but simply because when I had issues with the discus it was usually a specific infection/parasite which I would deal with using the specific medication for that.
To be honest if I was thinking of using 2000 with discus I would check as many reviews and forum reports etc to see if there are potential issues.
I have had excellent results with Esha Hexamita in my discus though.