I'm so new at this, but I found this in another forum in response to "white stringy poo disease"
"Stringy feces are due to intestinal Nematodes. Chances are you either have Camallanus or Capillary Nematodes. Both are easily controlled with Levamisole HCl. Camallanus are shown by red pricks sticking out of the anus of the fish. Theu can cause stringy feces that obscure them. One has to look closely to see them. Capillary are not so easy to find. Usually they cause the symptoms you report. Camallanus fills the intestine and body cavity with worms. Capillary just waste away the fish because they infiltrate the muscle tissue.
There aren't any medications on the LFS
shelf that is strong enough to get rid of these Nematodes anymore because the low dosage has generated super bugs over the past decades."
Hopefully this will get you somewhere