I have a community aquarium 200L stocked with various ancistrus bristlenose, cory, platy, guppy. For the past 4 months I have had individual isolated deaths. No marks on body or previous disease. Treated for flukes, worms, etc put uv steriliser in tank. Parameters NH3 0, NO2 0, NH3 5, pH7.5 GH5 KH15...

I recently obtained some "gold laser" cory from another fishkeeper. On adding them to my quarantine tank I noticed that one of them has quite a pronounced curve on the caudal peduncle, it goes down then up when viewed from the side bit like this ~ . Another has a slight curve but the rest ...