I don't remember if you said if you were aging your water? Do you temp match? 100% daily changes with unaged &/or unheated water could be stressing your discus, especially if the pH diff between your source water and your tank water is >0.4.
Also micro bubbles can stress discus so if you're filling straight from tap to tank and you see microbubbles on the glass I would recommend you aerate your water change water overnight even if the pH diff is <0.4.
Are the black worms live? If so, that is a bad sign not to eat live foods...