I pour 2 or 3 large bottles of peroxide in my medium-sized Koi pond, once a month. It's about a 950 gallon pond. It cleans the water and removes some of the algae build up. Not 1 fish has died and they are the fastest moving Koi/goldfish (I have a mix) I've ever had.
My great uncle took a tablespoon every day and lived to be over 100.