so how sensitive are our systems really?

[Aquattro]

My temps have swung from 79 to 89 daily for a summer. My salinity has hit 1.030 for a month. I've got rusted hose clamps in the sump going on 4 years. I've put my arms in the tank while covered in paint/oil/asst muck. I left lights on 48 hours. My skimmer shut off for 2 weeks. My CO2 tank drained into the room over a 6 hour period. I've used tap water without regard for chlorine. I test annually, needed or not.
All these things and many more, and the tank was rock solid. An established tank, and even a new tank well tended, are very rugged things.