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Mps Allergy


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Could be the hot water. If she has the same problem with a hot bath (and you need to keep it hot, just as is done in a spa), then it could be the heat. You can look at this link to try and distinguish between a chemical reaction vs. a bacterial infection. A doctor should look at it to be definitive, but it sounds like the reaction comes on quickly so sounds more physical/chemical than bacterial.

You could try a bath that is hot. Then try one with a tiny amount of Spazaaz to it. Then try a tiny amount of Dichlor. I doubt it's the salt.

It is possible to have a chemical sensitivity to chlorine, but it is very rare. Is your tap water chlorinated, or is it chloraminated (monochloramine)? You can use your test kit to see if you register FC or CC with your tap water. If she is able to take showers and you register FC in the tap water, then it's unlikely to be chlorine that is the problem.

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It sounds like, and looks like a chemical reaction. Our source water is chlorine neutral, If we switch to liquid chlorine, (ie. bleach) could she have the same reaction to it? Her rash is only where the jets hit her back, legs and arms. I really doubt this is bacterial, between the ACE system and the weekly shocks, the FC level never drops below 2ppm at the least, if there is a high bather load that day, and that is quickly corrected with dichlor. How much and what kind of liquid chlorine should we use to take the place of the dichlor? She has a Dr. appt. in the morning so maybe he can tell us for sure if it is bacterial or chemical. Thanks for your help.

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Using bleach with no Cyanuric Acid (CYA) in the water will be too harsh since the active chlorine (hypochlorous acid) level would be too high. Dichlor is a combination chemical that in water becomes CYA and chlorine (and a combination of chlorine-attached-to-CYA chemicals). If you were to use the ACE system and never have any CYA in the water (such as that added by the Dichlor), then the active chlorine level would be too strong. You should have around 30-40 ppm CYA in the water to moderate chlorine's strength.

Since your source water has no chlorine (is it well water? most municipalities add either chlorine or monochloramine to the water for disinfection in the mains), then maybe her reaction is indeed to chlorine. On the other hand, the rash on her back where the jets hit it would indicate physical irritation at least exacerbating the problem.

Did you ever try not using the Spazazz?

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  • 4 years later...
On 12/29/2014 at 6:42 PM, chem geek said:


I am not certain if hydrogen peroxide will neutralize MPS the way it most certainly does with chlorine. Though the thermodynamics say that it should occur since MPS as an oxidizer has a potential of +1.85V large enough to overcome the potential of hydrogen peroxide as a reducer of -0.695V, I do not know if the reaction is kinetically favorable. If it is, then the amount to use would be the same amount of hydrogen peroxide you would use to lower FC and in fact if you were to measure Total Chlorine (or FC+CC) then you could use that as your reference amount where the same volume of 3% hydrogen peroxide neutralizes FC from an amount of 6% bleach.

So in 400 gallons every 1 ppm FC would need 0.83 fluid ounces of 3% hydrogen peroxide to neutralize it. You probably don't have more than 5 ppm FC equivalent of MPS in the spa. In fact, I'm surprised if after two weeks you have any MPS left unless you haven't used the spa at all in that time and had added a bunch of MPS (maybe too much) after your last soak.




Has anyone tried this? I am wondering if you would still recommend this to get rid of MPS or is the “wait and see option” still ok?  I just refilled my tub and switched from bromine to chlorine thinking that was irritating me, but no change, skin eczema if back with a vengence first soak and I have perfectly balanced water. I went in two different hot tubs that weren’t mine and no reaction. I have good levels of sanitizer and have only used muriatic acid to lower TA (have you heard of reactions to this?). I have looked into MPS as the cause but figured since I always put it in after I soak it shouldn’t bother me. Any chance there is leftover sulphates that would bother me? And any way I could get rid of them without draining my whole tub? I should also mention I use the trio startup softener kit- maybe that is bothering me? But I assumed no. 

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  • 3 months later...
On 12/29/2014 at 4:42 PM, chem geek said:


I am getting a rash a day or two after I get out of our spa. My husband has changed the water and chemicals numerous times and I am still getting the rash. The bumps show up on my face, head, behind ears, chest & back. Not below where the water is so it has to be from the fumes, air. 

Anyone know what this could be? All I see is rashes from the water.


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  • 7 months later...

We bought a caldera salt system spa about 4 months ago. I’m having the same issue with a horrible rash all over my body and it gets worse the more I use the hot tub. We’ve drained it 3 times and its also good for about a week then rash comes back. I’m really frustrated with this. We spent a lot of money on this spa and I just can’t go in it. Not sure where to go from here. Also the dealer has been zero help. I’ve had pools and hot tubes my whole life and never had an issue. I’m wondering now if it’s actually something with the salt system and the chemicals mixing with the salt. 

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Sorry, I just picked up this thread, so maybe this has been mentioned already.

You have a saltwater spa?

You have an ozone generator? And are smelling ozone from your spa?

You are shocking with dichlor?

You are maintaining a constant 3-5ppm chlorine? With your chlorine generator/ "salt cell"?

Is this an inground spa?

If not, what brand is it?

If so, what control system does it have? Is it a fiberglass or plaster spa? Do you also have a pool sharing the equipment?

How much water does it hold?

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