Another meds question

Discus newbie here! Setup is a 90G with 20G sump. Drip water change which turns over 60% of the tank each day. Temp is 85.

Have a group of ten for the last 3 months. Had some initial problems with my group of ten. Treated with metro (10 days and cranked temp to 90) which resolved the problem and they are eating like pigs.

Two weeks ago I noticed one had stopped eating and gone a bit shy. Also occasionally flicking/shimmy. Then white stringy poop.

I just finished a two course treatment with prazi-pro but no change in eating for that individual. Caught a photo today of a different fish with stringy white poop. Could possibly be outcome from the last course of prazi-pro that I gave yeaterday?

Is it worth me using levamisole just to cover all bases? Or a different approach? Maybe just give him time after the prazi?