Wow, that's scary. My fingers are crossed for you.
I think I would have put in some H2O2, as used for a whole tank algae treatment, just prior to sealing. It releases a lot of oxygen as it reacts. I've used it along with heavy aeration to more quickly reverse the effects of CO2 overdose. Not sure if it's necessary or even effective here though.
Life happens. On semi-hiatus, checking in infrequently.