What is causing this & how do i treat it? for gill flukes ..
Gill and skin fluke
Flukes are external parasites. They usually attack fish gills and skins.
They look like worms and reproduce rapidly in an overcrowding tank with high organic content and stress.
Formalin solution: 40liters water in 1ml of Formalin.
Water change and redoes every 3 days for 3 treatments.