FWIW - I wrote & posted this about using H2O2 in containers a number of years ago and several times since. H2O2 has an extra O atom (compared to H2O) in an unstable arrangement. It's the extra atom that makes it useful in horticultural applications. Generally, we're not concerned with aerobic forms of bacteria normally occurring in container media or on roots. Since H2O2 is an unstable molecule, it breaks down easily. When it does, a single O- atom and a molecule of water is released. This O- atom is extremely reactive and will quickly attach itself to either another O- atom forming stable O2, or attack the nearest organic molecule. Reduced O levels and high temperatures encourage both anaerobic bacteria and fungi. Many disease causing organisms and spores are killed by O, and the free O- H2O2 releases is very effective at this. Additionally, when plants growing in water-retentive media are treated with H2O2 it will break down and release O into the area around the roots. This helps stop the O from being depleted in the water filled air soil air spaces until air can get back into them. High O levels at the roots will encourage rapid healthy root growth and discourage unwanted bacteria/fungi. I know H2O2 comes in several different strengths, the most common of which are 3% and 35% solutions. Least expensive is the 35% product (what I use) which you dilute (to an approximate 3% solution) by mixing 1:11 with water. I have used the 3% solution at 1 to 2 tbsp per gallon as a cutting dip/soak, and have mixed it into irrigation water for plants in extremely water retentive soils at up to 3 tbsp per gallon, both with good results and nothing adverse apparent. H2O2 in high concentration is a powerful oxidant and quickly oxidizes almost anything it contacts, so be careful with it if you use it. A solution that is too strong can destroy any organic molecule it contacts. I've seen this chart posted several times as suggested strength solutions for use in watering plants. You may wish to start at a lower concentration , such as I've used, and experiment. TO THIS AMOUNT OF WATER ADD THIS AMOUNT OF 3% HYDROGEN PEROXIDE --OR-- ADD THIS AMOUNT OF 35% HYDROGEN PEROXIDE 1 cup, add 1-1/2 teaspoons ... 35% - 7 to 10 drops 1 quart, add 2 tablespoons ... 35% - 1/2 teaspoon 1 gallon, add 1/2 cup ... 35% - 2 teaspoons 5 gallons, add 2-1/2 cups ... 35% - 3 tablespoons plus 1 teaspoon 10 gallons, add 5 cups ... 35% - 6 tablespoons plus 2 teaspoons 20 gallons, add 10 cups ... 35% - 3/4 cup plus 1 tablespoon plus 1 teaspoon 1) you can use them together w/no problems, but you shouldn't need it if you're watering correctly & the gritty mix is made even CLOSE to the suggested recipe. 2) Plants are reactive organisms. They will reach favorably to increased O2 in the root zone, and unfavorably to reduced levels. If you use excessive amounts of H2O2, it can kill viable tissues, so don't over use it. 3) Your plants won't get addicted to H2O2 to any greater degree than they are addicted to water. I would urge you to lift the plant from the pot & take a look at the roots to see what's going on, then prune roots back to sound tissue if you find rot as an issue. At that point, a dunk in a solution of H2O2 or unscented household bleach might be an appropriate measure. Al

H2O2 has an extra O atom (compared to H2O) in an unstable arrangement. It's the extra atom that makes it useful in horticultural applications. Generally, we're not concerned with aerobic forms of bacteria normally occurring in container media or on roots. Since H2O2 is an unstable molecule, it breaks down easily. When it does, a single O- atom and a molecule of water is released. This O- atom is extremely reactive and will quickly attach itself to either another O- atom forming stable O2, or attack the nearest organic molecule. Reduced O levels and high temperatures encourage both anaerobic bacteria and fungi. Many disease causing organisms and spores are killed by O, and the free O- H2O2 releases is very effective at this. Additionally, when plants growing in water-retentive media are treated with H2O2 it will break down and release O into the area around the roots. This helps stop the O from being depleted in the water filled air soil air spaces until air can get back into them. High O levels at the roots will encourage rapid healthy root growth and discourage unwanted bacteria/fungi. I know H2O2 comes in several different strengths, the most common of which are 3% and 35% solutions. Least expensive is the 35% product (what I use) which you dilute (to an approximate 3% solution) by mixing 1:11 with water. I have used the 3% solution at 1-½ to 2 tbsp per gallon as a cutting dip/soak, and have mixed it into irrigation water for plants in extremely water retentive soils at up to 3 tbsp per gallon, both with good results and nothing adverse apparent. H2O2 in high concentration is a powerful oxidant and quickly oxidizes almost anything it contacts, so be careful with it if you use it. A solution that is too strong can destroy any organic molecule it contacts. IÂve seen this chart posted several times as suggested strength solutions for use in watering plants. You may wish to start at a lower concentration , such as IÂve used, and experiment. TO THIS AMOUNT OF WATER ADD THIS AMOUNT OF 3% HYDROGEN PEROXIDE --OR-- ADD THIS AMOUNT OF 35% HYDROGEN PEROXIDE 1 cup, add 1-1/2 teaspoons  35% - 7 to 10 drops 1 quart, add 2 tablespoons  35% - 1/2 teaspoon 1 gallon, add 1/2 cup  35% - 2 teaspoons 5 gallons, add 2-1/2 cups  35% - 3 tablespoons plus 1 teaspoon 10 gallons, add 5 cups  35% - 6 tablespoons plus 2 teaspoons 20 gallons, add 10 cups  35% - 3/4 cup plus 1 tablespoon plus 1 teaspoon Al

grandmapoo, I use it for string algae, but also not feeding the fishes will help to cut it back (I think of my fish as little water goats at times; munching away on the sides of my pond). Cut back on any feeding and let the good bacteria in your pond catch up to the needs. Also I have heard it makes a wonderful way to introduce O2 into a water system when the O2 levels are low. LP Here is a link that might be useful: GardenWeb - Bumper crop of string algae

I don't know what else you are doing in combination with the hydrogen peroxide, but I have used 500-1000 ppm in my hydroponic water for years and have none of the symptoms you mention. Many other hydro growers have the same results I do, so I would suspect some other problem with your growing methods.