Transparent or white stringy poo is often associated with an internal problem, usually bacterial or protozoan.
Make sure the tank is clean and the water quality good. If everything is ok then look up Hexamita as it quite often infects discus and angelfish.
cheers Colin
the discus are very active and eating well so I've been happy there cos I know from many years ago when I kept them that I had trouble with one or two with feeding etc. Temperature is up and regular water changes.
I';ll check Hexamita out