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Help: some chemical causing allergic rash from hot tub

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I've had a little luck with Spa Selections Moisturizer. In the winter I get really dry, itchy skin on my calves and my wife gets rashes on her bathing suit lines.

We put it in before most uses and both of us seem to be a little better now. It does have a mild, pleasant fragrance, but some people hate having any fragrance at all. I was especially concerned about screwing up the water chemistry and tub cleanliness, but neither has been a problem. It's relatively cheap and enough of a help that I will probably keep using it. Nothing beats lotioning after, though. Good luck.


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this is a good opportunity to "over purge" if you will, to help rule out the factor of biofilms.  one thing we know -- you got better.  So you could still have biofilms in your spa.  all automatic dis

@dlleno true very good point; I was going to ask about leaving the ahhsome in overnight and I think it's a wonderful idea. I hear you on putting the filters in after we think we got most of the gunk;

Oh No....o yuk is horrible and very weak (read my blog i tested this head to head with ahhsome.).   Even the label directions indicate that the company is clueless .  They dont know how biofilms work

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2 hours ago, meh64 said:

I've had a little luck with Spa Selections Moisturizer. In the winter I get really dry, itchy skin on my calves and my wife gets rashes on her bathing suit lines.

We put it in before most uses and and both of us seem to be a little better now. It does have a mild, pleasant fragrance, but some people hate having any fragrance at all. I was especially concerned about screwing up the water chemistry and tub cleanliness, but neither has been a problem. It's relatively cheap and enough of a help that I will probably keep using it. Nothing beats lotioning after, though. Good luck.


Do you have a bromine or chlorine system.  Do you experience excess foam?

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On 2/12/2021 at 6:14 PM, dlleno said:

Cass -- you made a very interesting observation -- that the problem gets worse over time, and that you can go four weeks now instead of two.  that tells me you have achieved partial success.  But to me it sounds like your skin is sensitive to the accumulation of something in the spa water -- for example maybe its just the total dissolved solids.  The only way to fix that is to drain more often.  There is also the accumulated CYA itself.   have you tried bromine (you could run a  bromine spa with zero CYA, although I don't know of anyone who has tried this...).     how about a silver cartridge with a low level of bromine?  

Hi @dlleno- yes to me it seems like since it was 1 person using it instead of two this last time, I got twice as much time out of it before having problems.  I agree it's something accumulating. I am unclear why CYA increases over use in my use case? I do not use dichlor and I just use bleach essentially once I set the CYA to 30ppm at fillup. When this skin problem first happened, I was almost positive it was CYA causing this because I used dichlor before and the spa company just told me to keep adding that after using it- which accumulated too much CYA, and the chlorine is too slow to respond thus causing bacteria etc etc. However, this was also one of the chemicals I've tested in the bath tub, even at double the ppm that's in the hot tub (I used it with chlorine also) so it's not a reaction to just the CYA itself. I definitely can't keep up draining the thing every month, nor would I want to from an environmental perspective.

I also get a ring rash around my wedding rings which have stone settings in them which accumulate something that makes me quite itchy and rashy over a few months. I do not have any metal allergies- so it must be skin and crap?

At this point I'm not sure what else to try besides bromine- I was going to try thoroughly cleaning the filters every single week after a thorough decontamination again with ahhsome, and see how far I get with deep cleaning filters often and use the Hot Tub Serum that I purchased a while back as required.

As soon as the weather is good enough I'm draining and doing another fill. 

PS @Apollothesunsounds like you have some control of your skin problems and I hope it helps @meh64! My husband has the same issue from sweating and working out- he stopped exercising in Covid and it's completely gone!! The hot tub doesn't seem to bother it at all though. 


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total dissolved solids will accumulate, i.e. all the byproducts of sanitation that don't end up in the air.  you could just drain really often.  sounds to me like you have a skin sensitivity that is fairly rare among spa users, so you'll have to take extraordinary measures.  have you tried bromine?

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On 4/29/2020 at 6:06 PM, Cassiemoreira said:

Hi RDspaguy!

We've never dropped under 1ppm of chlorine on this fill (we decontaminated per the directions here at second fill), although on our first one we had some real trouble until we found your forum here and followed all the recommendations. The spa shop really sent us barking up the wrong tree. Now our water is crystal clear!

Presently we have 3ppm chlorine, 0.5ppm CC, CYA @ around 30ppm, TA is 120, calcium hardness about 75, pH 7.4, and temp of the tub is kept 99-100. 

Our water has a very high TA from the tap (250), so it took a LONG time to get it to come down, but finally did, just felt like we had to add a lot of acid and to get it to come down then had to add soda ash to get the PH back up a bit. 

Thank you all so much, I'm truly at a loss here and would appreciate ANY recommendations at all. 


Hi Cassie,

reading back at your post, i wanted to share my refill experience last weekend.  

I did a refill last saturday after using the spa guard enzyme on Friday.  It was comfortable while in the tub, had a little foaming but i knew my water was tired and decided to decontaminate using aaawhesome and super clorinating to 20ppm. Drained, wiped dry then proceeded to use gel gloss to protect the fiberglass. sprayed downed to flush any residue, with wet dry vacuum.  

Went to refill and before i added anything to the fill water, i went ahead and got a baseline with my test kit.  previously i was using the dip test strip but wanted to erase any doubt about what my fill water is.  Coming straight off the hose from city water,  

Ph 7.2, calcium 450ppm, chlorine .5-1ppm, alkalinity 50ppm, borates undetectable, cyna not detectable.

first thing i noticed right away was my high calcium.  I should be in the 150-200 range.  Previously i would add half a cup of calcium due to the test strips readings and it caught me off guard.  I have since purchase a pleatco pre-fill water filler to do top offs and for the next water change fill up.

so i went to adjust my chlorine level to 10 but accidentally put to much dichlor using the spa calculutor and shot up to 20 ppm.  so i decided to say screw it and adjust the chlorine level the next day while the tub was heating to temperature.  I proceeded to adjust the alkalinity to 80 and borates to 50.  Then the next day at water temp of 101, i decided to add hydrogen peroxide 3% to lower the chlorine to 8 ppm so i can use.  Testing cyna was at 60 and aerated till 7.5ph.  Added a capful of spa enzyme and I went to enter the spa.  I noticed the water was way comfortable than previous sittings.  I noticed that i was able to sweat right away and when exiting i did not feel any on set of itching.  Although i cant adjust the calcium right now, i will definitely take more notice on my next refill.  i did notice calcium deposit on my fiberglass water line previously too before draining. 

Nitro Dichlor/Bleach method recommends calcium at 100-150ppm.

Just a thought, maybe taking a look at your calcium level?

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On 4/29/2020 at 6:53 PM, Cassiemoreira said:

MPS for shock once a week 

MPS is a known sensitizer and is often the culprit in skin irritations. Stop using it completely after a fresh fill and see what happens.

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First of all a salt tub IS chlorine. Post a full set of test results and tell us what chemicals you are using, including any non chlorine shock products, borate products, etc. Also realize that some people will develop contact dermatitis from the hot water itself. Is your salt generator working and do you have a chlorine reading? Does the tub also have ozone. Many factors at play and you have provided no information.

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  • 1 month later...

I am having the exact same issue as @Cassiemoreira!

We have only had our tub for a year and a half and have had no issues with it until right after Thanksgiving. My husband took over hot tub maintenance while I was out of town visiting family. Well he was supposed to take it over, in reality he forgot. Next time I use the tub I get a terrible rash under my arms, on my hips, and ribs (basically where ever the jets hit my skin). This has been happening ever since and only to me (my husband has never gotten a rash). The rash never lasts longer than a day or two but is very uncomfortable!

I have drained and decontaminated several times using various methods found online, each time I am able to use the tub without much irritation for the first day or so, but inevitably it gets worse to where it was before the drain.

I was so optimistic when I found this forum and the decontamination method, I thought finally someone knows what to do!

Last week I went through this process, using ahh-some and a high level of chlorine to get the gunk out (I had a very minimal amount of stuff come out) then super chlorinated with bleach, drained, wiped down, refilled. 

After the first use of the tub I was fine, no rash or itch, but by the second use I started to see little red bumps under my arms and last night after a third use the rash was back and I had trouble sleeping due to the itch. 

I am so disheartened to hear that Cassie has still not solved her problem and am beginning to believe it is hopeless for me as well. 

I'll continue to decontaminate and drain (which I am doing on a monthly basis at this point) hoping that eventually I'll get out whatever it is that is causing the rash, but I'm starting to feel like whats the point? Is this worth my crazy high water bills when it doesn't seem to be doing anything? I wish I knew what else to do. 😔

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@nightmara I have similar issues...owned tub for 3 months no issues...then I started getting a rash.  Granted I didn't have a kit and was using test strips only.  I decontaminated according to Nitro's instructions, and this time went fully test kit and bleach method (20-30 CYA) as instructed...after a few times still got rash.  The only thing I'm guessing now is maybe instead of biofilm I'm allergic to the high chlorine content (I'm erroring on the high side of for chlorine since I was convinced it was biofilm).  My chlorine demand is very reasonable at 20-30% over 24 houts. 

I'm going to try again in a couple weeks as I let my rash die down and I'm going to keep my water extremely balanced.  I'm going to make sure my FC is no higher than a 4.  If I still get a rash after EVERYTHING is balanced...I dunno what to do next.


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Chlorine is not a sensitizer and, in fact, "bleach baths" with a concentration of around 50 ppm chlorine are often recommended to treat eczema in children and adults so I would look for another source.




Are you using MPS? This has been known to cause skin irritation. It could also be 'hot tub itch' which is a skin infection caused by Pseudomonas aeruginosa which normally comes from under sanitized water (which could happen by either not testing enough or depending on strips) and once established in a tub can be difficult to eradicate since it can form biofilms that are chlorine resistant. HIgher FC levels and not lower are normally recommended and it does not always affect everyone using the tub.



Finally, some people have or develop a sensitivity to the elevated water temperatures in a hot tub that results in a rash (Hives).



Would you mind posting a full set of test results and how they were obtained? (strips, liquid or tablet reagents, OTO, DPD, or FAS-DPD sanitizer test if liquid or tablet, whether a meter was used to read the results and whether it was dealer or home testing.) This way we can get a better idea of what is going on.

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@waterbear Thank you for the thoughtful reply.  Most of the three months I've been using test strips only until I decontaminated the tub 3.5 weeks ago.  Below is a quick timeline:

Dec: Got tub, filled it.  Used it only on the weekends (friday, sat, and maybe sunday).  I don't use it during the week because of work, so kept temperature at 80 during the week then bump it up to 103-4 thursday night for friday night and weekend usage.  After sunday, I would turn it down to 80 again.

Jan to end of Feb: Same usage.  Kept chlorine and ph balanced...but used only aquachek test strips.  Not testing anything else.  Frequent use of Dichlor and MPS only.  

March: Started having rash.  Itchy dry spots.  After a couple of days into the week, stopped itching and near end of week it would start to disappear.  Weekend comes, used tub...rash came back.  It could be a number of things...did a lot of research on bleach method, biofilm, balance with TA, CYA, hardness...these are things I didn't really adjust too much

3/20: Nitro decontamination.  Got ahh-some (see my post history) and purged.  Got Taylor K-2006 kit.  All test from now going forward is using this kit per instructions.  Tested everything.  Balanced water to the letter.  Used Bleach method and light on dichlor.  Got CYA up to 20-30 and all bleach after.

3/27: First use after decon.  Don't seem to get rash.  Used it twice that weekend.  Nothing noticeable.

4/3: Used it Friday and Sat.  After Friday seems dry itching came back a little but not sure.  Sat used again...sunday morning rash came back.

Been on top of checking most things.  Please see attached tracking log.  All tests are from Taylor K-2006 kit.  I only use MPS once a week now.  If Chlorine is not a cause, the hot tub itch seems like a possibility...could my recent decontamination/purge not get rid of it???  Hate to do it again, but should I purge again?  Let me know if you want to know anything else.  2026381054_Hottublog.thumb.jpg.8fbaee863f28b457a702ec1db28f5227.jpg

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 Hi @waterbear, one thing came to me is your other response below on my old post on temperature...especially the last sentence.  I don't use Nature2 but it occurred to me that I turn the temp down on Sunday night to 80...it takes about 2-3 days to get from 100 down to 80.  Only circulation is the "filter cycle" runs twice a day, once per 30 minutes the other time for 1.5 hours (2 hours a day total) during those three days.  It just came to me that this may be the cause?  Since it takes 2-3 days to cool down, biofilm may have more time to grow?  My tub uses friction heating so if I keep temp lower, it wouldn't circulate...only until it needs to maintain temperature would it turn on.  I wonder if I kept it at a higher temperature or if I lower the temp slowly, it would circulate more often.  I've since then adjusted the duration of the filter cycle to 1.5 hours each (total of three hours a day).  Thoughts on this?


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bottom line, if the water is not moving it's stagnant and things can grow in pockets of stagnant water that can cause a local depletion of sanitizer in those areas. As an experiment I suggest totally stopping the MPS (shock with bleach)  and NOT turning off the tub for about a 2 week period (after a shock)  and see if the problem still exists. If your CYA is 30 ppm or less shock to 15 ppm FC. if it's 30 to 50 ppm shock to 20 ppm FC, You can enter the tub once the FC is below 10 ppm.

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