Frustrating issue persisting despite emptying and refilling

[Perp]

We purchased a 700L two-person hot tub 5 months ago. The regimen recommended by the seller is a mineral stick, 10g granulated chlorine once a week (dissolved in 10L water, pour off chlorine, don't put granules in), 10g spa shock after every use (and at least weekly if not used more often), absolutely no bromine. Adjust pH and alkalinity weekly per test strips, test monthly at pool shop and adjust pH, alkalinity, and hardness.

The first 3 months we had no issues - water was always pleasant, only required minor adjustments.

Then we went away for a week. Having chlorinated the day we left, and leaving it to filter daily, we anticipated no problems, but when we got back it smelt absolutely rank - like a fish tank. (Algae?) Took a sample to the pool shop and they said the water was fine - pH, alkalinity, and hardness all in acceptable range - despite the stench. We tried chlorinating it a bit more - added an extra 20g - and the stench didn't go away.

So we ran the recommended pipe cleaner through the pipes, emptied and refilled the spa, made sure both filters thoroughly clean, put in a new mineral stick.

New water got smelly within days, and the pH shot up sky high - over 9.0! I got a terrible rash all over, my doctor thinks from the high pH. Spent about a week adding acid every day, did pH test, was down to around 7, then the next day it would be back up to around 9. 😒

Pipe cleaner, empty, refill again, and the same thing is happening - it smells fishy and the pH shoots up to 9 every day.

The shop that sold us the spa tell us to just keep testing the water and adjusting it, but it seems to me that something must be broken or not working for this dramatic change in behaviour, and for it to continue going drastically wrong every day. What might be broken to cause the pH to keep shooting up to 9?

[RDspaguy]

I've got nothing on the mechanical side. @waterbear, anything you can think of?

[waterbear]

Please post a full set of test results and we can take it from there. If you can also get a set of test results on your fill water. I have some suspicions but don't want to say anything until I see your water parameters.

I don't think the rash is from high pH. It is not uncommon in an undersanitized tub and just about every tub with a mineral sanitizer is undersanitized since there is not enough residual chlorine in the water and it can be quickly exhausted and bacteria can then grow. Smelly water is a give away.

https://www.healthline.com/health/hot-tub-folliculitis#outlook

I will say to get rid of the mineral stick and if you want to use chlorine read this post:

https://www.poolspaforum.com/forum/index.php?/topic/23090-dichlorbleach-method-in-a-nutshell/

Once again. post your test results so we can see if I am on the right track (not the first time I've come across this problem, btw.)

 

[RDspaguy]

I would be very interested in hearing the results of removing the mineral stick, as there should be no issues related to it if it is used properly. I have used them for many years and never had a problem. It can create a slight odor, as any metals in the water will, but I would not describe it as a fish tank like odor by any means.

Granted, they do not eliminate the need for sanitizer, or keep up with new contaminants (which you should not have much of with your cover on) but definitely reduce the necessary sanitizer residuals in my experience.

I am no chemist, or scientist of any kind, but I have been working on spas for a living for 25 years and have had many hundreds of happy mineral stick user customers over the years. And, just for the record, I do not sell (or even carry in my truck) chemicals of any kind, including mineral sticks. I have never made a dime from the maintenance products I recommend.

On the subject of new contaminants... It is not unheard of for your spa to get used by your neighbors while you are out of town. I once agreed to handle the water maintenance for a customer who was going out of town for several weeks. Every time I came by there were a half-dozen or so neighborhood kids in it, and the water was trashed. At vacation rentals in Tahoe it was quite common to find trashed water and empty beer cans all around when there were no guests checked in since the last time I was there. Just a thought...😉

[waterbear]

The problem with mineral sanitizers (whether based on Nature2 technology (silver/copper and very low Free Chlorine levels) or Frog (Silver/Zinc or just silver and used with low levers of bromine)  is that there is not a lot of residual sanitizer in the water (N2 only requires .5 ppm residual, which is quickly consumed  by just one or two bathers in the tub leaving only the silver and copper which have very slow kill times, have no effect on biofilms or viruses which leaves you with basically unsanitized water with an algaecide (silver, copper and zinc are all algaestatic). The frog system has a similar shortcoming. The use of metal ions for water purification comes from drinking water treatment and they are effective there because the contact time is very long  so they will eventually kill pathogens and  don't have to be fast acting since there is not a constant reintroduction of pathogens (particularly enteric ones, E. coli, giardiasis, cryptosporidiosis) from fecal matter on the bathers no matter how clean they THINK they are. Reality is that they are not and each one will introduce fecal matter and sweat, which is almost chemically identical to urine, into the water.

A chlorine or bromine system without a mineral system will run at a MUCH higher sanitizer level which provided quick kill times and enough residual sanitizer to handle the contaminants introduced by each bather. Remember, the volume of water in a hot tub is very small compared to the bather load and the temperatures are high. These provide an excellent medium for the fast growth of pathogens unless there is enough FAST ACTING sanitizer to help prevent this. As far at that goes Crypto is very difficult to kill, which is why fecal accidents in commercial pools require closing the pool and bringing the FC levels very high for several hours. In hot tubs Crypto is even harder to kill! and a mineral system is just not up to the task! Ionizers and copper sulfate based products were once very popular alternative sanitizers. However, they were not EPA approved sanitizers because they did not work on their own or with only MPS. Many countries either outlawed them completely or required they be used with chlorine at the same FC levels as used in a system without the coppper. Copper and copper silver systems will keep the water clear because algae won't grow but that's about it. Silver will have a bacteriastatic effect but with very slow kill times and no effect on viruses.

This is why I am not a fan of ionizers, "mineral" stick systems (the minerals being silver nitrate, copper sulfate, and/or a zinc sulfate), or all the copper sulfate based "Blue" products(Clearwater, Pristine, etc.,  and even IonRX which is,to the best of my knowledge, a chelated copper but not copper sulfate but still adding copper ions which they call "free ionic copper" and is meant to be used with very low FC levels) in both powder and liquid form sold as 'alternative santizers. I won't go as far as to call them snake oil but they make claims that don't hold up in real world use!

 

(rant over, getting off soapbox now)

 

[RDspaguy]

I've read the depletion time charts on various contaminants with regards to silver (with NO chlorine), and many were quite long, some even in the double digits of hours. That seems to be the main arguement against them, but I don't see why. I am perfectly ok with an 18 hour timeframe, as my spa is unused for 22 or so hours each day and I add chlorine after use, which destroys most if not all contaminants anyway. Plus, as another article I read (wish I could find it, I've read so many in the course of arguing with a few people on the subject) states, any depletion time represents a cessation of reproduction of the pathogens. If they are being reduced, then they are not increasing. In my opinion, that is what it does for you. Keeps the nasties from growing while your chlorine (and ozone) does it's thing, allowing for less overall chlorine demand and a residual of as low as .5ppm FREE chlorine AFTER treatment. 

As you point out, .5ppm is gone as soon as your foot hits the water, so you in effect have a "negative" chlorine level at that point. When you add chlorine after use you need enough to overcome your "negative" and result in a .5 or higher fc residual. This is guesswork, of course, as you can't really test "negative".

Of course, I also use ozone, which conveniently burns off chlorine in excess of .5ppm (the reason they picked that number for the mineral stick recommendation I'd think). If I test .5ppm free chlorine or higher, my water is good as any contaminants in the water would combine that fc and leave 0ppm free chlorine. 

I have had this same discussion with others you know, @waterbear(I won't drop any names) and still can't get on board with your assessment. I know you are much more knowledgeable on chemicals and such than I will ever be, but I still can't understand your opinion on this. It seems contrary to everything I have read from every other scientific source.

Sorry to sidetrack your thread @Perp. I hope you are learning something from this. 😉

[waterbear]

A History lesson. When N2 first came out it only used MPS and NO chlorine. We carried them and sold them. Copper/silver ionizers were very popular despite the fact that they stained pools. tubs and people green and they did not use chlorine, There used to be many 'alternative' copper based sanitizers on the market (ususally with Blue in the name) that did not use chlorine. There was a small group of pool and spa enthusiasts that questioned the safety of these products and, as a result they now have either been taken off the market, outlawed (in some countries), or require a minimum residual of .5 ppm FC . Ever wonder why? Perhaps it's because they didn't keep the water sanitized and metal ions do not kill viruses. Ever wonder why the EPA only has approved 3 sanitizers (chlorine, bromine, biguinide)? Maybe it's because they work! (Sorry for those using only peroxide without biguinide or trying to use only ozone, Peroxide is only an oxidizer, not a sanitizer and ozone has no residual but I digress)

.5 ppm FC is not really high enough for a hot tub because of the small volume of water involve vs. bather load but might be ok in a pool with a much larger water/bather load ratio. Every bather entering a tub WILL introduce feces no matter how clean they think they are and .5 FC is NOT enough to oxidize this, not the sweat and urine also introduced by each bather. Copper, Silver, and Zinc are NOT oxidizers. They work well in water treatment for potable water because the  CT is long and no further contaminants are introduce during the treatment but this does NOT hold true in a hot tub where contaminants are being introduced into a small volume of water with each bather and the residual oxidizer/fast acting sanitizer is quickly exhausted leaving nothing but slow aciting metal ions.

This is the hard science. If you want to soak in someone else's bacteria, viruses, and waste products do so by all mean. I prefer to soak in santiized water.

[RDspaguy]

💡 Ok. You are talking about the contaminants just introduced during this use, not anything "left over" and multiplying in the spa water from last time. Now I get what you are saying @waterbear; I might be affected by my own contaminants, or those of the others in the spa with me. Kinda like bathing with my wife in the bathtub?

I'm going to pm you for more discussion, as I have completely hijacked @Perps thread!