I guess to err on the side of safety is the right way to go, but I doubt 8oz of 8% will have any medicinal effect in 40 or 50 gallons of water.
The recommended amount of 35% H202 to start with in a tub of water is 8oz.
While I don't suggest anybody else do more than their comfortable with, I regularly use 32oz of 35% in a tub of water with no problems.
The downside is the expense. I pay $200 for 4 gal. Get 16 baths at a cost of $15 per.
The upside is how I feel after a bath. All aches and pains are gone, and I feel relaxed and refreshed.
Do the aches and pains return? Sure if the underlying problem that is causing them are not addressed. In my case, 50 years of heavy metals, and Antibiotics
given for chronic sinus infections. Working on the detox, hope it don't take fifty years to get rid of them.