Chlorine As A Shock???

[Quickbeam]

Hello,

My wife has some serious chemical sensitivities, so we have been using hydrogen peroxide as a sanitizer. For the most part it works fairly well, but every once in a while I find I need to shock the water. Up to this point I have been using a chlorine free oxidizer to shock but just recently I was having some trouble maintaining the water so I tried a chlorine shock put out by SpaLife called “Clor”. On the ingredients it lists “Lithium Hypochlorite” at 29% and “Available Chlorine Content” at 35%.

I have a couple of questions regarding this “Clor” product. First of all, if I use say one tablespoon in a 350 gallon spa, set at approx. 102 degrees, could anyone tell me how long it would take for this to dissipate from the water?

I’ve also read somewhere that when chlorine is added to the water it creates a buildup of CYA. Will this happen with this product? Are there any other by-products that are left behind from using this?

Thanks so much for any help you may be able to provide.

[Dr. Spa™ Ret.]

How sure are you of her "serious chemical sensitivities"? More people are allergic / sensitive to non-chlorine shock (MPS) than any other chemical used in spas.

[Quickbeam]

Very sure. Her sensitivities are real and they are serious. I didn't use the non chlorine shock very often, and when I did she would always wait a minimum of 24 hours (usually longer) before going in the tub again. I was also told that the non chlorine shock would dissipate after 20 minutes. Maybe that's not correct, but that's what I was told.

Can anyone comment on my original questions re the chlorine shock?

Thanks.

[chem geek]

Lithium hypochlorite will not build up either CYA (like Trichlor and Dichlor) or CH (like Cal-Hypo).  It's basically the same as bleach or chlorinating liquid but in a solid granular form.  It's pretty expensive, but for a spa the quantities are much lower and you're only using it as a shock to keep the water clear.

HOWEVER, realize that chlorine and hydrogen peroxide react with each other where chlorine gets neutralized to chloride salt while hydrogen peroxide gets neutralized to oxygen gas and water.  So to do a chlorine shock you'd need to dose with an excess of chlorine.  Then when you are done shocking, adding an excess of hydrogen peroxide will dechlorinate the water.

As for MPS, what you were told is incorrect.  It does NOT go away in only 20 minutes unless there is a lot for it to react with.  Generally, it lasts even longer than chlorine in a spa because it reacts with fewer chemicals and does so more slowly (it doesn't react much with ammonia, for example).  It's usually MPS that is irritating to some.

So if your wife is sensitive to chlorine, do you have a dechlorinator for your shower or a whole-house carbon block filter to remove chlorine and chloramines?  I know you've told us about the sensitivity before but I don't remember how you dealt with it outside the context of just the hot tub.

[Quickbeam]

Thanks Chem Geek,

For answering my question. I’m not entirely sure however that I understand the part about chlorine and hydrogen peroxide reacting with each other. I’ll tell you exactly what I did the last couple of days.

I knew there was something wrong with our tub water as it was eating more hydrogen peroxide than normal.  The water was clear, but it was definitely using more H2O2 than it should. It had been doing this for a while. I think I’ve mentioned before that our spa is at a cabin, so I shocked with the MPS just before we were leaving for a week. When we got back to the cabin I did my water tests and the tub had been using H2O2 at a rate of 23 ppm per day. This was not quite as bad as when we had left, but still much higher than it should be.

That’s when I decided to try shocking with the “Clor”. I added 2 tablespoons of Clor. I had thought that this amount was probably excessive, but this water problem had been present for a while and I wanted to see if the chlorine would clear it up. I tested the water 24 hours after adding the two tablespoons of Clor and the tub had only used 5 ppm of H2O2. It looked to me like the chlorine had fixed the problem but I was concerned about how long it would take for the chlorine to dissipate.

I normally do all my water testing with a Taylor test kit (K-2106), but don’t believe with my test kit I can test for chlorine. (Note that I purchased extra reagents so I could test for H2O2). I did have some old test strips that I got with the spa and after I did my regular water checks for H2O2 I used the test strips to test for chlorine. This was 24 hours after I added the shock. I’ve never used those test strips before, but from what I could see there was no chlorine present in the tub. I certainly could not smell any chlorine present in the tub, but how long would I normally have to wait until say 2 tablespoons is dissipated? Our tub is 340 gallons.

So given what I’ve described above, is this what I should be doing if I’m shocking with “Clor” or am I missing something? It looks to me like what I did worked, but again I’ve never used chlorine before so I’m just not sure. And if the chlorine and H2O2 react with each other, why would the tub only use 5 ppm of H2O2 after 24 hours?

Quite honestly, if the chlorine works this well, and it dissipates quickly, then I’m thinking I could use it as a shock after every soak. I was thinking of maybe adding one tablespoon after every soak??? As long as it dissipates before we go in the tub again, then I’m not sure I see a downside, or again am I missing something?

And finally, to answer your questions about filters for our house, we do not use a whole house filter. My wife does however have a filter on her shower and she also filters all her drinking water.

Thanks again Chem Geek for taking the time to answer my questions. It is very much appreciated.

[chem geek]

The K-2106 tests for Total Bromine which also tests for Total Chlroine and you can't distinguish between these.  It also shows hydrogen peroxide so again you can't distinguish between any of these three with that test kit.  Even MPS shows up so really the test is for Total Oxidizer.

As for hydrogen peroxide and chlorine, they react with each other to neutralize each other.  So depending on how much chlorine you add and how much hydrogen peroxide you had you end up with one or the other but after a minute or so you cannot have both simultaneously.

I don't know exactly what test strips you used that tests for hydrogen peroxide.  It's possible it's a unique test for that which is not interfered by chlorine or MPS, but I don't know.

Chlorine does not dissipate quickly by itself.  It does decline but mostly it's your adding hydrogen peroxide that gets rid of it.  So think of it as ping-ponging back and forth between having a hydrogen peroxide spa and a chlorine spa.  If you didn't add excess chlorine and added less than the amount of hydrogen peroxide in the spa, then you simply use up the chlorine you add to the spa so there's not much point doing that.  If you want to use chlorine to oxidize things in the spa that hydrogen peroxide doesn't handle, then you need to add an excess of chlorine to both get rid of the hydrogen peroxide and have extra left to oxidize what's in the spa.  Then you can add hydrogen peroxide back to get rid of the chlorine and build up hydrogen peroxide again.

To do this back and forth you need a test kit that can test for chlorine separate from hydrogen peroxide.  A Free Chlorine test kit (something with a DPD test) will test for chlorine and may have interference from hydrogen peroxide if the level is high enough.  You could experiment with test kits and known amounts of chlorine vs. hydrogen peroxide to see how they show up.

As for why the tub didn't use as much hydrogen peroxide after the chlorine treatment, you may have had something in the tub that built up and created a hydrogen peroxide demand and when you added chlorine it got rid of it faster than what hydrogen peroxide can do.  It is not uncommon to use chlorine periodically in bromine tubs or in Nature²/MPS tubs to keep the water clear.  Chlorine is a good oxidizer to keep the water clear.

If you want to use chlorine you should do so when you've got the hydrogen peroxide level lower and then dose enough to have chlorine for a while.  Then when done add hydrogen peroxide to get back to that before your next soak.  You could probably do that just once a week.  If you were to just do this after a soak it would likely just waste both chlorine and hydrogen peroxide.

[Quickbeam]

Thanks Chem Geek.

[Quickbeam]

Chem Geek,

One final question if you don’t mind. Is there something else I should be using as a shock in an H2O2 tub? I would be looking for something that would not react with the H2O2, would dissipate in a reasonable amount of time and would not create a build up of anything else (eg - CYA). Does such a product exist? Thank you.

[Quickbeam]

Chem Geek,

One final question if you don’t mind. Is there something else I should be using as a shock in an H2O2 tub? I would be looking for something that would not react with the H2O2, would dissipate in a reasonable amount of time and would not create a build up of anything else (eg - CYA). Does such a product exist? Thank you.

Would bleach work?

[chem geek]

Bleach would do the same thing as Dichlor in terms of reacting with hydrogen peroxide.  The only difference is that Dichlor will increase the CYA level while bleach will not.

If MPS (non-chlorine shock) were great at oxidizing bather waste, then that might be an alternative, but it generally doesn't do as well as chlorine.  Bromine likewise doesn't do as well as chlorine.  The only thing I can think of that you might be able to use are enzymes IF they can tolerate the hydrogen peroxide level.

[Quickbeam]

Thanks Chem Geek.