What all params did you test at the time? How did the pH and KH sit? It does sound very contaminant-like. Was anything else unusual used in the house? Any sprays/aerosols used or brought by anybody? It's also not impossible that someone could have put a hand in there that had bad stuff on it (various skin care products, soap, etc.). But, it won't be the being up late part; I have a hard time keeping my tanks on a strict schedule as most don't have timers, but nobody has kicked the bucket yet from me sleeping in by accident or staying up late.
Are you running carbon on the tank? It's a good idea to run a fresh batch in the event of a mysterious event like this, even with big water changes, just to make sure you scrub the water as much as possible.
EDIT: man I just can't seem to post properly today. I'm editing everything right after I hit the darned button because I forgot half of what I was going to say! Anyway, the reason I ask about the params in more details is that if you're not sure if it was something spilled in, you really want to try to eliminate other environmental possibilities like atmospheric contaminants to minimize the chance that it happens again randomly at some other time. There's also the unlikely but still possible "nudi nuke" and "cuc nuke" types of events with toxic hitchhikers dying that can give a mysterious tank crash that only affects certain animals but not others, although the events of that nature that I've seen gave very unique test kit readings (e.g. some tests just turned funky, nonsensical colors).
Are you running carbon on the tank? It's a good idea to run a fresh batch in the event of a mysterious event like this, even with big water changes, just to make sure you scrub the water as much as possible.
EDIT: man I just can't seem to post properly today. I'm editing everything right after I hit the darned button because I forgot half of what I was going to say! Anyway, the reason I ask about the params in more details is that if you're not sure if it was something spilled in, you really want to try to eliminate other environmental possibilities like atmospheric contaminants to minimize the chance that it happens again randomly at some other time. There's also the unlikely but still possible "nudi nuke" and "cuc nuke" types of events with toxic hitchhikers dying that can give a mysterious tank crash that only affects certain animals but not others, although the events of that nature that I've seen gave very unique test kit readings (e.g. some tests just turned funky, nonsensical colors).
