I did my 50% water change today, everything was fine.
2 hours ago I check on the boys, Venom's tail looked tattered and torn.
I decided to take him out of the divided tank and into a 1gal, I added my conditioner. Within the hour, his fins are nothing but strings and black/goopy.
The only thing I can think of is this is a new bottle of conditioner, he's been fine the last 2 weeks.
*sigh* he's in clean water now with epsom salts... I don't think he'll make it to the morning :(
Could this be a defective bottle?
Edit to add: ammonia is at 0, it's an established tank. pH are constant with what they've always been.