If you setup the ozone correctly -- Then its impossible to overdose the ozone.
The key factor is how you apply the ozone. Along time ago before the days of skimmers we would pump ozone directly into the display tanks using wooden air stones. And in those situations you could pump to much ozone in and then overdose.
Ozone is highly unstable, it doesn't want to exist, so as soon as it gets the opportunity to break apart from O3 it will. Basically as soon as the O3 physically bumps into anything it breaks apart.
This can be easily accomplished by spilling the ozone infused water and breaking it over a piece of live rock or a container of carbon/sand.
I have been using 500mg/hr ozonizers for over 10 years. I previously had one on my 240 Fish only tank (before I took the tank down). And I have one that runs on my reef system. They run 24/7 uncontrolled and without issue.