Yeah, I know :oops: ...I'm a bit of a stickler for water changes :lol: Sunday is put aside for tank cleaning and water changes and it takes me all day if I let it :lol:
And you're right, it doesn't explain sudden deaths. I don't think it was the water change causing shock either because it was only 15%.....unless the water was contaminated somehow? Just a thought.
It is most likely that it's been caused by the Cardinals introducing something but, I'm sorry, I have no idea what.