I also believe that with good aeration by surface agitation by a spray bar or surface skimmer or an airstone.
This thread is a good read to understand why we can suffocate our pets:
http://www.barrreport.com/showthread.php?t=10282
Next time, take seriously the fact that you can kill them. Choose a way to do it that is not at the edge of a catastrophe.
My condolences.