This is getting too muddy for me. I will quote you, and leave it at that. I hope you have good luck with the remaining egg, and look forward to updates.
" One of the eggs died. I think I killed it during a water change. "
(And then the others died, possibly due to medication, etc?) That's not a firm system. If other people are coming in, possibly using chemicals etc, that's an open system, not a firm one.
This is just honest, positive feedback: I think if you gained better control of the environment surrounding the tank, and inside of it, you'd have better results all-around. I will second that you should take it easy on medications, and focus on maintaining good water quality without being too disruptive during water changes.
I have had fish labs, I've had nature classrooms in schools, with many tanks, as well as tanks in my home, etc. If you worry about power outages, get a generator, OR keep them in a place where you can be there, and actually know if the power goes out. Glass covers and educating people who come into contact, about the use of chemicals, takes care of the risk of chemical usage that may harm your fish. It all comes down to common sense, really. When doing water changes, do it gently, and obviously don't let the new water flow right next to, or on, the fish / eggs.
People tend to over-think things - it's in our nature - but in ALL cases, common sense should be prevalent.
That said - I'll get off my horse and hope the last egg pulls through, and hope you can create a firm system
