Yeah it just seems odd that the tire track had died from that when he was in a tank just like it before but I tested water chemistry and it wasn't good for nitrate so with one fish dying even from a different cause I just wanted to look into everythingI'm confused....are you concerned about the water quality then too? because the eel obviously didn't succumb to water chemistry issues. if the fire eel is behaving normally then I would forgo adding a bunch of water treatment at the moment...