Ok, so i suspect internal parasites. Here's how to treat
Internal/intestinal parasites:
Symptoms - Internal parasites are also “worms,” but these target a fish’s intestines. As a result, the main symptom is white stringy poop. It has to be white; brown stringy poop, for example, can just mean intestinal irritation which requires no treatment.
Treatment options - API General Cure (a medication containing both praziquantel and metronidazole). Some species of internal worms are resistant to prazi, while others are resistant to metro, but usually not both. :wink: Seachem MetroPlex can be dosed directly in QT, or soaking fish food with it provides an alternative (and reef safe) treatment option. Two other available options are: Paracide-X (mixed in food) and Paracide-D (in-tank treatment).