Perplexed. No Free Chlorine Measurement

[BrianMc]

We just got started with a hot tub this summer. We bought a Hot Spring Vanguard. The dealer told us that once we get the water balanced the standard maintenance was to simply add a teaspoon of chlorine granules each time we used the tub. Well, I had been checking the water regularly during the summer when we had more visitors and I found that I needed to add a few teaspoons each time. Once fall hit and it was just my wife and me using the tub, I started adding a teaspoon each time as the dealer had suggested. I wasn't checking the chemicals regularly.

Last week, my wife got a bit of a skin irritation and I figured I better start monitoring the chemical in the spa more closely. I adjusted the PH and then tried to get the chlorine right. I was adding a teaspoon at a time and the free chlorine indicator was not moving. I tried super chlorinating -- 5 teaspoons and still couldn't get it to move. I tried it one more time. No free chlorine indicated -- but oddly enough(to me anyway) the bromine indicator was measuring levels of bromine (3-5 range). I've never used bromine in the spa and as I recall the indicator has never shown any bromine levels. But the indicator said the level was OK.

Yesterday, I brought a sample of the water to the dealer for analysis. He said things looked good aside from no chlorine. He told me to add 3 teaspoons of the chlorine granules (Regal Dychlor-II). I went home and added 5. No free chlorine. Today I took another sample to the dealer. He said I had "chlorine lock" and that was why the indicator was showing bromine but no free chlorine. He said to hit it with a couple lids full of MPS chlorine free oxidizer and wait a few hours and then hit it with chlorine again. I waited 5 hours after the MPS treatment. I checked the water before hitting it with chlorine. It still showed bromine. I hit it with 5 teaspoons of the chlorine. The test strip now shows Total Bromine (TBr) over 10. No free chlorine (FCl).

The dealer is closed. I'll get in touch with him tomorrow. But in the meantime, I am very puzzled and wondered if anyone might shed some light on what's happening. Thanks.

[Nitro]

I've never heard of "Chlorine Lock" before, maybe Chem Geek can fill us in, if there is such a thing.

However, it sounds like yet another classic example of a dealer not giving you the full story. "To add a teaspoon of chlorine granules each time we used the tub" is not enough to keep the tub sanitazed, especially if you have more then two people in it. The fact that your wife got a skin irritation (rash) MAY mean you need to decontaminate your tub. At the very least you should change your water, and start over.

The first thing you should do is go here and read. If you have questions, ask away.

[chem geek]

The most likely possibility is that you didn't use enough chlorine when you and your wife were soaking so you built up ammonia/urea in the spa from your sweat/urine. The chlorine you added produced some Combined Chlorine (CC), specifically monochloramine. Any chlorine you now add is simply converting ammonia to monochloramine and any MPS you are adding is oxidizing ammonia directly, but it's not enough. This would explain why adding more chlorine doesn't show up in the chlorine test assuming that test is measuring Free Chlorine (FC), but it does show up in the bromine test because it is probably measuring Total Chlorine/Bromine including CC. It sounds like you are using test strips so I'm guessing here as to what these particular strips are doing.

"Chlorine Lock" isn't real in that its just a description of a seemingly insatiable chlorine demand, but in reality its just a situation such as what was described above or could be (for pools) algae growth consuming chlorine (not likely the case for a spa). The other thing that can happen is that continued use of Dichlor builds the Cyanuric Acid (CYA) level so high that oxidizing the CC takes many hours.

If you really want to know accurately what you need to do, you should get yourself a better test kit such as the Taylor K-2006 you can get at a good online price here. The FAS-DPD chlorine test in this kit will accurately tell you both the Free Chlorine (FC) and the Combined Chlorine (CC) levels. In addition to this kit, you can get an inexpensive ammonia test kit from an aquarium/fish/pet store.

Basically, you need to add enough chlorine or MPS to oxidize all of the monochloramine and ammonia. Every person-hour of soaking at 104F in a 350 gallon tub needs roughly 3-1/2 teaspoons of Dichlor or 7 teaspoons of MPS or 5 fluid ounces of 6% bleach. If you and your wife were soaking for 40 minutes, you probably should have been adding at least twice as much Dichlor (a little more than 2 teaspoons). If this was going on for a month, then it could take 30 teaspoons of Dichlor or 60 teaspoons of MPS to clear the situation -- that's not really practical.

Of course, at this point, it might just be easier for you to do a water change since it's probably time for you to do that anyway. As Nitro noted, you should decontaminate your tub since the skin irritation may indicate that the hot tub itch bacteria has already taken hold.

Richard

[Nitro]

"Chlorine Lock" isn't real in that its just a description of a seemingly insatiable chlorine demand, but in reality its just a situation such as what was described above or could be (for pools) algae growth consuming chlorine (not likely the case for a spa). The other thing that can happen is that continued use of Dichlor builds the Cyanuric Acid (CYA) level so high that oxidizing the CC takes many hours.

That's what I was thinking, but I wanted to make sure there wasn't some magical phenomena going on as this particular dealer seems to be portraying. What's really scary is that they named it, like it happens all the time to their customers. "Oh that's just 'Chlorine Lock'. No big deal, just add some MPS and it'll fix 'er right up." Meanwhile Brian's wife's skin is melting off. Sorry to be sarcastic, but this kinda stuff annoys me.

Brian, I would not take my chances using that tub without a good decontamination. HERE is where you'll find the procedure. Basically you're going to add ~1/2 gal of bleach to your tub and let it run for 30-60 mins, with all jets on. Then drain and refill. Also, checkout the link I gave you earlier. It will explain everything you need to know to keep your tub safe using Chlorine. If you have any questions, please ask.

[BrianMc]

Thanks for the assist, Nitro and Spa Geek. I've ordered the water test kit -- those strips are frustrating. I'm off to Pet Smart in the morning to get an ammonia test kit. I'll read up on the decontamination business and the regular maintenance routines. I'm not getting the warm and fuzzies about the information my dealer has been giving me. I was told with the ozone system on the spa that I would only need to change the water once a year. I'm remembering a cartoon from my youth where a gullible lion is taunted repeatedly with the shout of "Sucker!!!"

[Nitro]

Thanks for the assist, Nitro and Spa Geek. I've ordered the water test kit -- those strips are frustrating. I'm off to Pet Smart in the morning to get an ammonia test kit. I'll read up on the decontamination business and the regular maintenance routines. I'm not getting the warm and fuzzies about the information my dealer has been giving me. I was told with the ozone system on the spa that I would only need to change the water once a year. I'm remembering a cartoon from my youth where a gullible lion is taunted repeatedly with the shout of "Sucker!!!"

ONCE A YEAR? Are you kidding me? I wouldn't listen to a word that dealer says.

While you're out getting that ammonia test kit, stop by the grocery store and buy a gal of bleach. I'd start that decon asap.

[1bad88]

Basically, you need to add enough chlorine or MPS to oxidize all of the monochloramine and ammonia. Every person-hour of soaking at 104F in a 350 gallon tub needs roughly 3-1/2 teaspoons of Dichlor or 7 teaspoons of MPS or 5 fluid ounces of 6% bleach. If you and your wife were soaking for 40 minutes, you probably should have been adding at least twice as much Dichlor (a little more than 2 teaspoons). If this was going on for a month, then it could take 30 teaspoons of Dichlor or 60 teaspoons of MPS to clear the situation -- that's not really practical.

Of course, at this point, it might just be easier for you to do a water change since it's probably time for you to do that anyway. As Nitro noted, you should decontaminate your tub since the skin irritation may indicate that the hot tub itch bacteria has already taken hold.

Richard

Richard,

Is the 7 teaspoons of MPS needed per person/hour of soaking the correct dosage if you are using a bromine feeder system, or is this only for a chlorine based system?

-J

[chem geek]

It's correct if MPS is the ONLY oxidizer you are using. If you have chlorine or bromine, then you'll need less MPS. So if you have a bromine feeder, then presumably there will be some bromine in the water. The question is how much. That's not easy to answer because bromine forms bromamine which is still a reasonably effective sanitizer, but I can't find anything on the rates of further oxidation. That is, I don't know if bromine can be used to oxidize bather waste (ammonia/urea from sweat/urine). If we assume that it's not much of an oxidizer, then the 7 teaspoons of MPS per bather-hour would be roughly the right amount.

Of course, you can just see how it goes and if you have a test strip to measure MPS you can see if you are using too much and scale back accordingly.

[Hillbilly Hot Tub]

What is the CYA at? Its got to be fairly high and all this adding chemicals is worthless. It also may be what is causing the skin irritation.

IMO water change....the only people that can get a year from water is those that have the salt generators that produce bromine or chlorine.

[Nitro]

I agree with HHT, dump the water, fill, THEN do the Decontamination, then refill again.

However, you could try putting in a "Spa Flush" to clean out the gunk in your pipes before dumping it for the first time. You'll be surprised how much stuff comes out.