Sounds like it was going OK for a bit though. Then it all fell apart. I would guess with an almost closed eco system that it doesn't handle issues that well and with a couple of issues that spells disaster.
I would have thought that if it was a water/oxygen issue there would have been some survivors so it was more likely a waste issue with all the waste raising the pollutants in the water especially when the water was reduced by 60+%.
Lessons learnt;
Don't feed them so much. (Trial and error)
Fix issues when they happen. (Sounds like you left the water down for some time)
Have backups available. (When something breaks)
Note I subtly didn't mention the communication problem with the missus.