I do exactly what the guy in the video did, H2O2 in a pump spray bottle, to kill off java moss in my 400 gal. system. 90% water change, then spray the background, rocks driftwood with hydrogen peroxide. Like others have said, H2O2 is relatively unstable and wants to lose that extra oxygen atom. It quickly breaks down into water and a free oxygen molecule. It really knocks back everything that is sprayed and I repeat at each water change
I've heard that H2O2 is sometimes used when bagging fish for a long trip, add the right amount and it raises the oxygen level and the fish are able to be in the bag longer. Not recommending anyone try that until you research how much is safe.