To begin, remember and ounce of prevention, yada yada. If a person already has a mess of pythium they are dealing with, H2O2 may or may not help their roots recover. H2O2 vs. Bleach is a long standing argument. I would rather not get into that aspect but I will say both are beneficial in non-organic Hydro systems.
Also, residual levels of both H2O2 and chlorine will vary a bit from individual systems depending on temperatures, aeration, concentrations of products used, and amounts of bacteria or fungi needing to be destroyed.
That being said, here are some basic guidelines.
H2O2
I use H2O2 for a preventative measure, as its a quite unstable molecule that releases one oxygen atom and one molecule of H2O as it decomposes. Because this this extra O atom is so reactive, it will either attach itself to another O atom (creating O2), or it will attack a nearby organic molecule. So it is a win win because when the H2O2 breaks down it will either increase the dissolved O2 in the res or it will kill unwanted bacteria.
There are many grades of H2O2, 3% 8% 17.5% 35%. I recommend steering clear of your local pharmacy's 3% as manufacturers add acetanilide to prevent the decomposition of low levels of H2O2 from occurring too rapidly. Instead use "Food Grade" H2O2, the higher the percentage, the more economical it will be. It is recommended to dilute to 3% prior to use as it is extremely caustic to use at such high concentrations.
Diluting to 3% will be determined by the concentration you purchase but to keep it simple, add 9 parts of distilled water to 1 part 30% H2O2, or 11 parts H2O to 1 Part 35% to get a 3% ratio.
1:9 for 30%
1:11 for 35%
After dilution I add 3ml per liter (2 1/2 tsp./Gal) of 3% H2O2 to every fresh reservoir and replace 25% daily for maintenance.
Ex. for 20 gal res. add approx. 1 cup of 3% H2O2 initially. followed by 1/4 cup every day for maintenance. For DTW, reduce maintenance amount by 1 tbsp/5 Gal. as necessary. H2O2 does not remain in the res for as long as chlorine.
Chlorine
I recommended initially shocking your reservoir with 2-2.5 ppm chlorine and dose with .5-1 ppm every 24-48 hours depending on system. If you already have signs of root rot or pythium it is ok to dose with a 4 ppm solution. Most tap water has between .7 and 2.0 ppm chlorine normally and federal law allows up to 4 ppm. Pythium starts to be destroyed at levels as low as .2 ppm. My research allows me to believe that chlorine will not harm plants in even higher concentrations in a non-organic system, but to avoid argument these levels work fine.
Its getting late so to keep it simple. Dilute H2O and Clorox Bleach 38:1-40:1 or approx. 1/2cup/Gal or 100ml/L
Add 5ml/L of diluted solution to res initially for 2 ppm. add 2.5 ml/L every 24-48 hours for 1 ppm. Add 10 ml/L for 4 ppm root rot destroyer.
Conversion
10ml/L = approx 2tsp/gal
5ml/l = approx 1tsp/gal
2.5ml/l = approx 1/2tsp/gal
Notes:
1. Use gloves and eye protection when using H2O2 ESPECIALLY high concentrations.
2. Keep diluted mix in opaque container to prevent rapid decomposition. Pressure does build as H2O2 decomposes so use strong container similar to a soda bottle.
3. Keep your H2O2 refrigerated to increase shelf life.
4. When buying H2O2, squeeze container to check for freshness. If you feel "cracking", buy elsewhere or return as H2O2 has already began to oxidize container.
5. Reiterate, 1 oz prevention = 1 lb cure
6. I have personally not found any information advising NOT to use chlorine and H2O2 together, however I recommend trying each individually as one may work better than the other in any given system. If signs of prolific fungi, bacteria, or root rot are present, I see no reason why a combination of the two would be harmful in a non-organic system.
Good Luck.
