(aside: I think it would be fun to work out if it's possible to use H2O2 as an additive to a system where the power has been lost to keep O2 levels from going too low. That would require knowing the breakdown rate which would depend on what organics/enzymes the H2O2 ran into. Too complicated to be actually useful, I think)
An Oxydator will do that, nay it has saved any number of aquarium.fish both FW and SW when under a power cut. As with peroxide dosing it will also oxidise ammonia. The Oxydator is such a simple device that has the potential to save an aquarium due to.kack of O2 and ammonia poisoning.