Hydrogen Peroxide After Chlorine Shock

[Spasome]

I've used hydrogen peroxide successfully a number of times to lower chlorine levels following a super-shock w/ chlorine bleach.

I'm wondering if there is anyone that is knowledgeable about possible byproducts remaining after this procedure.

1) I use hydrogen peroxide from the pharmacy isles at Costco and unscented Clorox. Are there any reasons (besides the cost of chemicals) to recommend limiting this procedure? In other words, will undesirable by-products build up in the water from excessive use of hydrogen peroxide to oxidize bleach regularly?

2) Are there other oxidizing compounds that are less expensive or that are more pure (less trace chemicals involved in the production). I am not familiar with the manufacture of hp or what the inactive ingredients may be.

3) Shelf life. I like to buy in bulk because it reduces cost but especially because it makes it easier to maintain adequate supply without running out at inopportune times. Does the potency of hydrogen peroxide diminish with time? How do the alternates compare? Storage is cool and dry.

One other related subject. I am very interested in learning more details about the chemistry of super-shocking to reduce combined chlorine levels. Occasionally, after careful testing (using the Taylor 2006 kit), and super-shocking to 12-15 times the measured CC level, the CC levels rise. Obviously I didn't use enough chlorine on those occasions. Is there any detailed reading available on this subject that is understandable by someone with only a basic understanding of chemistry? I would like to know more about the actual chemistry as well as practical tips to increase effectiveness while not shocking to unnecessarily high levels.

I really enjoyed the recent article that was recently linked here about how the misconceptions the pool industry had regarding the validity of slugging vs. spreading acid depending upon the effect desired. It surprised even me that such an established industry could hold onto invalid ideas for so long.

Thanks for any insights anyone can contribute on these subjects.

[chem geek]

Reducing chlorine levels by using hydrogen peroxide is very safe since it just produces oxygen gas, water, and chloride salt as follows:

H₂O₂ + HOCl ---> O₂(g) + H⁺ + Cl^- + H₂O

Hydrogen Peroxide + Hypochlorous Acid ---> Oxygen Gas + Hydrogen Ion + Chloride Ion + Water

As with other times when chlorine oxidizes a chemical or gets broken down in sunlight, it's a net acidic process, but the pH went up when the chlorine was added so the above just drops it back down to where it started.

When you are using hydrogen peroxide to reduce chlorine levels, the hydrogen peroxide is being used as a reducing agent, not an oxidizer. Yes, it is an oxidizer, but when chlorine is around, chlorine is the stronger oxidizer and oxidizes the hydrogen peroxide. The typically 3% hydrogen peroxide you get is decent stuff with the rest just being water. There usually aren't bad impurities. You can also get more concentrated product as Baquacil Oxidize Shock which is 27% hydrogen peroxide (do NOT get the CDX product, which is different).

Storing hydrogen peroxide in a cool place is best and it is very, very important to keep it away from sunlight. The UV in sunlight will break it down. Oxygen in the air will react with hydrogen peroxide so after you open the bottle the shelf-life drops from one or more years to months (figure 1-2 months to be safe). Most quality hydrogen peroxide contains stabilizers in the form of metal sequestrants since metals can degrade it, similar to chlorine.

Superchlorination simply accelerates chlorine reactions. Even regular chlorine levels will oxidize inorganic chloramines and more slowly oxidize some organics. So shocking to a higher chlorine level doesn't always work. If you've got a lot of an organic that is slow-to-oxidize, a higher chlorine level may just form more chlorinated organics that measure as Combined Chlorine (CC). Usually when this happens, the compounds don't smell and and are not generally a problem. Not all CCs are created equal. So in practice, soon after a water change, the chemicals from your sweat and urine get oxidized by chlorine when you add it to the spa water. Over time, some of the chemicals that are slower to oxidize build up and when they do the CC can build up as well. Eventually you change the spa water.

Now if you are using Dichlor-only, then the Cyanuric Acid (CYA) level will build up making the active chlorine level lower (at the same FC level) and this can slow down chlorine's oxidation of even the moderately easier chloramines and if that happens, you can get smell from the chloramines. Also, the water can turn dull/cloudy sooner and you would then need to change the water sooner than if you had properly managed the CYA level such as by using the Dichlor-then-bleach method.

As for invalid ideas in the pool/spa industry, you should read the post I wrote: Certified Pool Operator training -- What is not taught.

[clarity guy]

If you are using H2O2 why do you need chlorine I have switched to 35% non food grade it is a hot tub I add about 2/3 a cup once a week ,if ph gets high I will add a cup of white vinegar.My neighbors have been using it for 2 years it is great easy to use and where some say it is expensive I find it to be a lot less than all the other chemicals I use to use just don't jump in your hot tub after working in yard rinse off and wash you swim wear with just water no problems 

[BigOlBandit]

I agree,  our bromine program was working fine but we didn't like the smell of skin after,  so based on what our neighbors had been doing for 5 years already,  we switched to a cup of 35% peroxide (costs $4/liter) twice a week and that had worked perfect for a year until a month ago we got some algae or something, so we shocked it with a dose of chlorine and now it seems we are back on track with the peroxide.    A year ago we originally used municipal chlorinated water,  when we changed it out 6 months ago we just used 1/2 hard water from well,  and 1/2 softened water,  and that seems to also work well.    We have learned that when our pH gets out of range the water gets cloudy but a correction gets it clear again.    And the number one thing we learned,  change the filter every two weeks.     

[Tmorin]

Hi,

My cure for going away from bromine & chlorine is hydrogen peroxide.  The only thing I had to add was a UV system.  Since I did this months ago & my water is crystal clear & I haven't had to change it.  My alkalinity & ph have varied only slightly & require infrequent adjustments.  I add hydrogen peroxide 2oz per 100 gallons initially.  I add an 1/2 ounce after each use unless its multiple people. Each weekend I add 2 ounces. If I notice any cloudiness at all I shock it with peroxide to bring it back to crystal clear 

The UV kills the germs & bacteria  (The sanitizer) & the peroxide handle to stuff from bodies... lotions, etc.  It is not a recognized sanitizer for spas even though it is one. It is an oxidizer which is its primary function for me with the secondary benefit of sanitation.  I also bought a 1/2 gallon of Bacquacil CDX as it bonds with peroxide to make it last longer.  only 0.3 oz per 200 gallons & I add it each time I put in 2 oz or more of hydrogen peroxide. I buy 35% hydrogen Peroxide food grade. 

I realize that UV systems are expensive. Mine had a 7 watt Balboa wavetec & the bulb replacement was too costly at over $120 per year & the unit was leaking. ($500+ to replace it)  This might sound crazy but I could not understand why  UV system designed for home ponds of well under 2000 gallons would not work. The principle is the same & they are far cheaper in cost & bulbs are less than 1/2 the cost (twice the wattage a well)  They work off cycling X amount of GPH & want  the volume of water  (volume of the body of water )to be circulated  within  1-1/2 to 2 hours. My tub is only 200 gallons & my circulation pump does 1.5 GPM which is under the 2 times threshold of the unit I bought. My spa does llow me to set circulation times. Plus I can look in & tell when the light needs replaced & clean the glass cylinder the bulb resides in twice a year.   My tub has no warranty left so I didn't have to worry about violating it so if yours does...check first. I also find rinsing the filters out with  hose (have a mineral canister filter attached to hose) once a week & cleaning them once a month works great. (I have two sets of two filters I swap when cleaning the ones that came out)

I love not dealing with chlorine or bromine. It smells like fresh hot water. One last note, I use baking soda to adjust alkalinity instead of paying for it in a different form. It only has a small effect on PH. When alkalinity is right PH stays better balanced especially with the UV killing on the DNA & RNA level & peroxide doing its thing.    Just my two cents on the topic.