Here are my two cents worth of experience with Hydrogen Peroxide:
My experience with H2O2 is with 35% from a hydroponic store, which I have used for about 15 years.
If you have plants that drain very slowly in soil, H2o2 will cure the problem. Plants that take five days to dry out in soil will dry out in 24 hours with a teaspoon of H2o2 per gallon in the water. Plants in soil can take more hydrogen peroxide without burning than plants in a hydroponic system because of the soil buffer.
In Hydroponics, when plants are small, H2o2 must be used hesitantly because you will burn them otherwise. I use about 1 tablespoon per 20 gallons for smaller vegetating plants with no problems. Hydrogen peroxide burns the little jagged edges of the shade leaves and in some cases the tips of the leaves if you over do it.
When plants are bigger in Hydro, I use two tablespoons per 20 gallons of solution with no problems.
If you have problems with algae growth on your hydroton or rockwool, add hydrogen peroxide when you top off your solution during the week. I add two tablespoons (for bigger or flowering plants) every time I top off my solution. Whatever algae you have will go away in a few days. Make sure you stir it in well so they don't accidently get a strong dose of undiluted to their roots.
If you have a sealed system, like an aquamist, I would suggest adding it when you first change out your solution and again midway between solution changes.
Hydrogen peroxide is awesome for cleaning out and sterilizing the system upon flush. When I clean out the system, I fill a five gallon bucket with water and add 5 or 6 tbsp of H2o2. I put my pumps and hoses into this bucket and run them for about ten minutes to sterilize them. I then use this water with a sponge to wipe down the whole system and sterilize everything clean as a whistle. I then fill the system, add two tablespoons of 35% H2o2 (to a 20 gallon system) and run it for a few hours to clean and sterilize everything, then I add my nutes.
It is best to err on the side of caution with Hydrogen Peroxide. A little too much can burn the shit out of your plants. I use very small amounts and get very good results. 2 tablespoons is about 30 ML which doesn't seem like much in 20 gallons, but if your system smells like fish tank water, the next day it will smell fresh as a daisy.
As far as bacteria are concerned, I could care less about them. I'm not into organics and just use the GH flora series nutes and get stunning results with no bacteria in my system. Of course, you might feel otherwise.
Don't spill it on yourself. Ouch. It doesn't burn for a few minutes but it eventually makes your skin turn white and burns like hell.