General Cure is a powder that works on killing internal parasites and external flukes as it has both metroplex + praaziquantel. If you mix the powder with food (flake, frozen, etc.) and Seachem's Focus (a binder) it will work especially well on internal parasites (worms) that are causing the white stringy poop. If the fish is not eating, just dose the General Cure, in a QT, into the water. Use a fine net. Pour the GC into the net. Massage the net to express the GC into the water. Some will remain in the net. That's ok. Just express the most possible and then turn over the net into the water. Some will settle to the bottom of the tank. Then wait 5-7 days. Do a 25% water change and dose again with GC. Wait 5-7 days. Do a 25% water change. Observe for 7-10 days. Sometimes another round of GC might be necessary but that is somewhat rare.