Sour smell.

[Nilking]

Hi.

Quick question, my hottub water is perfectly clear and doesn't smell at all. Chemistry is fine according to my tests.
BUT, after a soak, when I'm drying it smells a bit sour from the skin. When completly dry the smell disapperars completely.
Any ideas what it can be?
I use Sodium Dichlor and Hot Spring MPS Chlorine-Free Oxidizer to sanitize the water...

[stuart]

maybe your getting old....

No I would add some more chlorine for awhile and see it helps

[Nilking]

You were right twice Stuart, I AM getting old and adding more chlorine fixed it.
Shocked it with 6 tabespoons of chlorine after consulting with my Swedish HS dealer, the problem is gone. I'm probably too restrictive with sanitizers..

Good thing that it worked, we are having the coldest winter here in 10 years.
I don't wanna empty/refill in -15C/5F...brrr

[just ducky]

I've noticed a bit of that smell now and then too.  But I try to keep the chlorine level at bare minimum, which probably accounts for the smell now and then.

[stuart]

If you leave the cover open for a few moments after shocking with chlorine it will gas off and go away for the most part. there is no reason to use it at a minimum if it doesn't stay there.

[chem geek]

Chlorine combines with ammonia in your sweat to form monochloramine which is probably what you were smelling.  Normally, if you have the chlorine level be around 1 ppm FC at the start of your soak, then you won't smell anything during the soak and after you get out.  The downside is that you won't have sanitizer present during part of your soak, but if you add it right after you get out then the risk is low since it takes 15-60 minutes for bacteria to double in population and presumably you are soaking by yourself or with family members and not those that could transmit disease.  Most people using either the Dichlor-only or Dichlor-then-bleach methods add their chlorine after the soak such that they measure a roughly 1 ppm FC residual at the start of their next soak.  This also minimizes your exposure to other disinfection by-products (DPBs) and as noted in the previous posts, keeping the cover off after adding sanitizer/oxidizer to the tub for some time (say, 30 minutes) will outgas the worst offensive DBPs.

[Nilking]

Thanks for the answers everyone.   
Chemgeek, I only use chlorine after a soak since my SPA has some kind of silver-ion cleaning + ozone. So before a soak I put in "SPAchock" to activate the Silver-ION stuff. Do you think that I still should have around 1-3 ppm? The following ( not meant to be a salespitch) is from my manufacturers web:

"FreshWaterAg+® Continuous Silver Ion Purifier
The FreshWater Ag+ continuous silver ion purifier further reduces the need for chlorine by introducing silver ions into the spa water that inhibit bacterial growth. Insert the cartridge into the filter of your Hot Spring spa, and the silver ions are released automatically - there's no chance of under- or overdosing. It's virtually maintenance-free - simply replace the cartridge every 3 months."

[just ducky]

I do leave the cover off for approximately 10-15 minutes after adding chlorine, which I do after each soak.  And during my weekly maintenance, I have the cover off for at least 20-30 minutes because I alternate through the various jets, and use the various air toggles to make sure I've cycled through all ports. 

When I say I like to keep the chlorine to a minimum, for the first few months of owning my tub the reading was consistently high. But with the help of my dealer and some of you on this board, I now I've gotten my chem maintenance figured out to where when I take a reading with the test strips, it normally reads a minimum of chlorine.  That's where I like it.  Am I playing with fire a bit?  Maybe.  But I just prefer to keep the chems to a minimum.  So far so good after nearly a year.

[chem geek]

Thanks for the answers everyone.  
Chemgeek, I only use chlorine after a soak since my SPA has some kind of silver-ion cleaning + ozone. So before a soak I put in "SPAchock" to activate the Silver-ION stuff. Do you think that I still should have around 1-3 ppm?

As to whether you've still got chlorine when you start soaking, that depends on how much you added after the soak.  The SPAchock is a non-chlorine (probably MPS as you said) oxidizer and with silver ion in the water it becomes an effective sanitizer as well (this is also the basis of the Nature2 low-chlorine recipe that mostly uses MPS with the silver ions fro N2).  If you use enough SPAchock to take care of bather waste during your soak, then the chlorine added afterwards might survive long enough to your next soak, though usually an ozonator will tend to deplete it.

In any event, the shocking with chlorine got rid of the problem (according to your post) so it may have just been that you weren't using nearly enough oxidizer and the water built up with your bather waste (ammonia and urea from your sweat and urine) so when you added chlorine that formed monochloramine.  What is strange, though, is that you didn't smell it during the soak and only noticed it on your skin -- normally that occurs when your sweat combines with chlorine.  Note that using Dichlor every day will build up Cyanuric Acid (CYA) making the chlorine less effective so you might consider doing something more like the N2 low-chlorine recipe which is to use the non-chlorine shock as your primary daily oxidizer/sanitizer, but use the Dichlor only weekly.  That should build up the CYA more slowly while still taking care of whatever the non-chlorine shock and MPS were not able to get rid of to keep the water clear.  Just make sure you don't let the MPS level get too low -- if you have MPS test strips you can use those.

The rough rule-of-thumb for the amount of oxidizer needed (when one does not have an ozonator) is that every person-hour of soaking needs around 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach or 7 teaspoons of non-chlorine shock (43% MPS) -- note that a person-hour isn't a minimum, so one person for 30 minutes (half an hour) would use half of these amounts.  This is independent of spa size and assumes a hot (100-104F) spa and average amounts of sweating.  Since it sounds like you have an ozonator, you wouldn't normally need to use this much oxidizer, but use the MPS test strips as a guide making sure there is still some registering before your soak (that is, before you add any more -- if it's too low, then you need to increase your dosage so it lasts until your next soak).

As a reference, you can see the Nature2 Owner's Manual though I would assume you have a manual for the specific system you have.

[Nilking]

Chem geek, thanks for the great answers.

Sour smell came back today, but not nearly as much as the prevoius time.
I'll guess that I have to add more dichlore after each soak, I will follow your "rule" and add 3 teaspoons/person of dichlore after a soak.
Hope the cold weather here goes away, I really want to refill my tub now and start over.

[chem geek]

It's 3-1/2 teaspoons per person-hour, not per person.  Are you really soaking for an hour in a hot (100-104F) tub?  Also, I wouldn't add more Dichlor.  Use more MPS instead and save the Dichlor for less frequent shocking (such as weekly), but remember that the MPS rate is double the Dichlor rate (i.e. 7 teaspoons per person-hour)

Also, are you sure your ozonator is working?  Usually with a working ozonator you won't be getting so far behind.  Also, I don't think you have to refill and start over if you haven't used the tub for very long.  How long has it been since your last water change and how much Dichlor have you added into what size of tub (in gallons)?

[Nilking]

Hehe, we soak for hours here sometimes in 101F/38C.
Weekdays we maybe soak for 30 minutes at a time, weekends maybe 1-2 hours but with shorter breaks.

Since I filled the tub first of november I've added maybe 1 kg/2.2 lbs* of chlorine granulate in it.
Ozonator is working (at least I get bubbles)
 
*I'm in sweden and used this site for translating kilos to lbs:http://manuelsweb.com/kg_lbs.htm

[chem geek]

If you added 2.2 pounds of Dichlor to, say, 350 gallons (1325 liters), then that's a cumulative amount of 417 ppm FC and 380 ppm CYA with the latter CYA not going away (much) so significantly reducing the effectiveness of your chlorine.  Since the 1st of November that's around 75 days so the chlorine usage was around 5-1/2 ppm FC per day and was around 1/2 ounce per day or enough for around 50 person-minutes of soaking.  You said "we" so I assume 2 people soaking, so on weekdays that's about the right amount of chlorine while on weekends probably not enough, but if your ozonator was working it might be OK.

HOWEVER, the very high CYA level makes the chlorine so ineffective that it's no wonder that everything all of your bather waste may not be getting oxidized.  If the ozonator were really powerful then maybe it could keep up, but your spa isn't really sanitary since the high CYA level makes the chlorine over 10 times weaker than at the normally recommended 30 ppm CYA level.

I'm not going to offer the Dichlor-then-bleach method for you since that is looked down upon on this forum, but I would suggest instead that you follow the normal water change rule which is to change the water after the following number of days: (1/3) x  (spa size in gallons) / (number of bathers) which is normally for 20-30 minute soaks.  So in your case, this is no longer than around 60 days or 2 months for weekday type usage, but your weekend usage pushes this more to 40-50 days.  If you used the Dichlor-then-bleach method, you could probably go at least twice as long before a water change, but that's not a traditional approach used on this forum and requires you to handle your water chemistry a little better (lower TA, use of 50 ppm Borates).

[Nilking]

Yep, waterchange as soon a the temp goes up...
Curious question here regarding CYA.
I'm following a swedish hottub forum and there one person said that we do not have CYA in our dichlor. (or more specific, dichlore for hottubs does not contain CYA)
Sounds suspicous. Isn't CYA one of the "biproducts" from dichlor?

Having a hard time here trying to translate the name of chemicals from swedish to english. I hope I get it right.. )

[Dr. Spa™ Ret.]

Cyanuric acid is one of the products REQUIRED to produce dichlor. Dichlor can't be made without it.