Help!! Odor (like chlorine) smell that makes you cough

[jcichocki]

With our indoor pool we have acquired a smell that makes us cough (seems like chlorine gas). Initially when we open the cover there is no smell. It seems most evident when the spa is started (either jets or bubbles). Lately, the odor seems to be obvious whenever we splash somewhat aggressively. The pool people were here looking at something else, and I asked them about it. They said the chlorine was too high. At the time it was (I had just shocked the pool). After the chlorine level came down, they diagnosed high phosphates. Now both things are normal and the smell still remains.

Against my better judgment, I went to the pool store to get a comparison number tests. Here are the numbers.

Pool store: FC 1.5 TC 3.0 pH 7.4 Alk 50
Me: FC 1.0 TC 1.5 pH 7.5 Alk 100

They said the smell was chloramines (CC?). They said either shock the pool or add GLB oxy brite. We had a bucket of oxy brite from the original batch of chemicals from the pool builder, so we tried it. They also said to raise the Alk.

This AM results: FC 2.5 TC 3.0 pH 7.5 Alk 100.

Any thoughts? It has gotten to the point where we don't use the spa because the coughing is too much. Thanks everyone!!

 

[JasonLion]

Your CC level is too high. CC is TC minus FC. You can eliminate CC by shocking, either with chlorine or a non-chlorine oxidizer. For indoor pools, MPS is usually the preferred way of getting rid of CC. Oxy Brite is MPS, so using that is a good idea.

What are you using to test the water? Having a top quality test kit makes this process much simpler. Given the smell you describe, I am more inclined to believe the pool store test, which shows a CC level of 1.5, compared to your test. A CC level of 0.5 doesn't normally have the effects you describe, but a level of 1.5 does. With your own top quality test kit you will be able to know exactly when you get rid of the CC, without additional trips to the pool store. I recommend a kit from TF Test Kits, see the link in my signature. The Taylor K-2006 is also good.

By the way, phosphates are almost never a problem. They are mostly a way for pool stores to scare you into buying expensive chemicals that you don't need.

It would be good to find out and post your other numbers, calcium and CYA in particular. CYA is not commonly used with indoor pools, but if you have been using the wrong products, the CYA level can get fairly high and that can make the chlorine ineffective. For an indoor pool, you want CYA to be between 0 and 20.

 

[jcichocki]

Thanks!! I had a bucket of oxy-brite from the pool builder and just put the last of it in the pool. I looked online to purchase more, it appears there are several brand names: Blitz, Impact, Shocktrine, Oxy-brite. Are they all the same??? I never know when when you buy generic cough syrup if you are really getting what you paid for. Of course, there is a tremendous range of prices. Since my pool is large I will need quite a bit, so it pays to shop around. Any further assistance would be great. Jeff

 

[spishex]

As long as the active ingredient is potassium monopersulfate or potassium peroxysulfate it'll do the trick.

 

[jcichocki]

Have added several doses of Oxy-brite. Still have the issue of coughing with the pool. Still have the elevated CC.

Latest readings: pH 7.5. TC 5. FC 3. CC 2. ALK 110. ORP 770 (went up from 630 after oxy-brite). Borax 50. Salt 1600.

Question is: should I shock with bleach to get rid of CC. No quick/significant change with oxy-brite alone? The non-chlorine shock seems to work great but not a quick solution to elevated CC?

Second question: can I use oxy-brite alone without bleach? Will it still result in a build up of CC?

Thanks!!! Jeff

 

[chem geek]

Unfortunately, any residual MPS is going to register on the test kit as CC (initially right after addition it can also register some as FC). The MPS should drop over time and perhaps you can look at your ORP readings and tell when that happens -- when they return back to where they were relative to your FC level (i.e. are no longer elevated). So it's possible that your current CC readings might be MPS. Is the smell still there, especially when splashing?

You can't use only MPS in place of chlorine, but you can use it as a supplement to try and avoid the formation of CC in the first place though without a special test kit it will be hard to know (there are test strips that measure MPS explicitly and there is an MPS interference remover from Taylor for the CC test, but some have not found it to be reliable).

There's another possibility, but I'd only expect it if you had some moderate-to-high bather load in your pool or vigorous swimming (lots of sweat) or some kind of urinary accident (children peeing in the pool). Has any of this happened? I suspect that what you are smelling is nitrogen trichloride and unfortunately that's a type of Combined Chlorine (CC) that does not readily break down by adding more chlorine (and may not break down from MPS either). Ironically, there is a way to get rid of it, but it's tricky so if you're game I'd like to try it with a bucket test before trying it in your pool.

Richard

 

[JasonLion]

Getting rid of CC in an indoor pool can occasionally be quite difficult. Here are a couple of things to keep in mind. Indoor pools need massive amounts of ventilation. Inadequate ventilation can sometimes lead to high CC levels or make it more difficult to reduce CC from other causes. The beathing problems you refer to suggest that there is inadequate ventilation.

MPS will cause ORP sensors to give higher than actual readings. If you are running ORP based automation, MPS can result in the chlorine level getting too low. For a couple of days after adding MPS, you need to compensate for this by readjusting your ORP set point based on drop based chlorine level readings.

CC can be eliminated with chlorine but it may take large quantities of chlorine and lots of ventilation. Outdoor pools are different. it is much easier to get rid of CC outdoors. If you have any way to get direct sunlight on the pool that would help.

 

[jcichocki]

Richard thanks. I'm typing this on my phone, so the reply will be short. Pool open for a year. This coughing problem had been a problem almost the whole time. Excessive splashing and especially the spa jets make the coughing horrible.

Bather load quite low. 2-6 people a few times a few. Minimal sweat, we have a baby but he is not in frequently and problem was present before he arrived.

Bring on the bucket. Will try anything!! Thanks.

 

[chem geek]

First, I'd like to acknowledge and reiterate some of the things that Jason said because if you indeed have nitrogen trichloride in your pool, then aeration of the water combined with lots of ventilation will remove it. Also as he points out, sunlight will break down nitrogen trichloride so exposing the pool to sunlight (UV light, actually) will also remove this irritant.

OK, now for the bucket test. Basically according to the best breakpoint chlorination model I have, nitrogen trichloride will not get broken down by additional chlorine alone, no matter how much you add. Ironically, it requires dichloramine or monochloramine to break it down -- that is, it requires the more basic forms of Combined Chlorine (CC). So for the bucket test, we're going to take pool water and add some CYA to it and some ammonia (and chlorine unless it's already there which I believe it will be). The reason for the CYA is to slow down how fast the chlorine will react because when chlorine is reacting quickly, it tends to produce more of the bad nitrogen trichloride while when it reacts more slowly it tends to allow the intermediate monochloramine and dichloramine to form thereby minimizing the amount of nitrogen trichloride that is formed. If all of that was over your head, don't worry about it.

NOTE: You should read the following instructions first to see everything you will need and to make sure you understand it all. I didn't write this in the form of a recipe.

So, first take two large buckets of roughly equal size and shape and fill both with pool water leaving some room at the top so you can stir without spilling. You need to either know or measure the volume of these buckets (actually, of the water in them, so draw a line at a known volume level). You will also need an additional bucket for diluting chemical additions, but it doesn't have to be the same size or shape as the others, but does need to have a known or measured volume. The dilution bucket should ideally be dark, even black, so that you can see any undissolved chemicals at the bottom more readily.

Get some Cyanuric Acid (CYA) either from a pool store or from a friend with a pool who has some -- you will only need a very small amount. Take 2 teaspoons of the CYA (which are usually small round pellets) per gallon of volume in the dilution bucket and grind them using a mortar and pestle or whatever other creative method you have for crushing them into a finer powder. Then, fill your dilution bucket with tap water and add the crushed CYA powder into it and stir until it is thoroughly mixed, which might take some time. If you see any residue at the bottom of the bucket, keep mixing. Now take one fluid ounce (which is 2 tablespoons or 6 teaspoons) per gallon of the CYA water from the dilution bucket and add it to one of the pool water buckets and then mix the water in BOTH buckets about the same way for the same amount of time. Use separate stirrers for each pool bucket (and probably for the dilution bucket as well).

Measure the FC and CC levels in each pool water bucket. I assume you will already have some chlorine in the water so just note how much that is. You'll want to increase the FC to 4 ppm so scale up the following dilution instruction which is for a 1 ppm FC increment (you only scale up the 2 teaspoon amount, not the one fluid ounce amount). To increase the FC by 1 ppm, you would add one fluid ounce (2 tablespoons or 6 teaspoons) of 6% bleach in the dilution bucket (emtpy it, rinse it out and fill with tap water first since it will still have CYA in it) and mix and then take 2 teaspoons of this mixed solution and add it to the pool water bucket where you added CYA and ammonia and then mix. Mix the other pool bucket in the same way and for as long.

Now, get some household ammonia and see if you can get some that has an ingredients label so you'll know the concentration of ammonia. Usually, household ammonia is 5-10% in strength though some are even less (3.5%). For the quantities I'm going to give you, I'll assume 10% strength so you can scale accordingly. Empty out and rinse out the dilution bucket with tap water and then fill it with tap water (to the known volume). Add one fluid ounce (2 tablespoons or 6 teaspoons) of ammonia and mix. Take 1/2 (that's 0.5) teaspoon of this mixed solution and add it to the same pool bucket where you added the CYA and mix. Mix the other pool bucket (that doesn't have CYA nor ammonia in it) in the same way and for as long.

Wait 2 hours and then remeasure the FC and CC levels in each pool water bucket.

Post your results. If all goes well, you should see the CC level much lower and hopefully getting close to zero. Then the trick will be to properly scale this up for your indoor pool.

The above essentially creates a mixture of 4 ppm FC with 20 ppm CYA and 0.5 ppm (as ppm N) ammonia where it is assumed that the 2 ppm CC is nitrogen trichloride (which is 0.4 ppm N). It turns out that the FC level isn't critical. What is important is having the ammonia amount be about the same (or a little higher) than the nitrogen trichloride amount measured in the same units. It's also important that the active chlorine level not be too high which is why I used CYA.

Richard

 

[jcichocki]

WOW!!! Seems like chemistry homework from 25 years ago. I will get to work tomooriw night and post the results. A million thanks in advance.

As fas as the ventilation, we think we have a very good system. The problem is not swimming for a few days and the auto cover is in place preventing off gassing.
Any idea what a good amount of vent time might be? Should we spent a few hours each night aerating the pool?

 

[jcichocki]

Almost forgot, is artificial UV lighting an option?

 

[chem geek]

Since you are trying to make up for a problem that has occurred over an extended period of time, you'll probably need to keep the cover off for days with the ventilation system running full bore and ideally you generating as much aeration as you can (turn the returns up with the pump running, for example). Note that your pH may rise from this so you may need to add acid as well as baking soda to keep the TA stable.

Once your pool is clear of CC, then probably venting it for a few hours (2-3?) each day might work, but my goal is to prevent the formation of CC in the first place so let's see how your bucket tests work. If the pool is unused for an extended period, then venting won't be needed though there is a time lag so venting for at least a couple of days after the last usage would still be needed.

As for artificial UV, that should work, though I don't know if it will be intense enough given the volume of your pool and the downside to it is that it will tend to use up your chlorine faster. Again, I'd prefer to avoid the creation of the nitrogen trichloride in the first place.

Richard

 

[jcichocki]

My wife spent about 10 hour venting and aerating yesterday. When I got home and collected the chemicals I began the bucketing.

Bucket test done!

Here is what I did, please check my procedure and math.

Pre-bucket pool readings: pH 7.6, FC 0.5-1, TC 2, CC 1-ish, TA 110, CYA ? lost black dot with tube completely full, scale only to 30, ORP 720 (as you suggested it has been high since adding Oxy-brite last weekend).

Tools: 2 - five gal. buckets and a 1/2 gal jug for mixing. I put 3 gal in each of the test buckets. Taylor test kit (K-2005).

CYA: 1 teaspoon dissolved in 1/2 gal tap water. (Absolute pain the A@*, mixing it). Added 6 tablespoons of mixture to my 3 gal of pool water. Mixed as directed.

Chlorine: 3 tablespoons of bleach into cleaned 1/2 gal tap water jug. Then 6 teaspoons added to pool water with CYA. Mixed. (I did test the FC here to make sure my concentration was right - appeared to be about 4 ppm).

Ammonia: Bought Walmart Crud without a concentration on the lable. Checked their MSDS online and it stated 2-3%, go figure. No wonder their prices are so good, no ammonia in the bottle! Anyway, I used 2.5% as my concentration. Added 4 tablespoons ammonia to cleaned, tap water 1/2 gal jug. Then 1.5 teaspoons of mixture to pool water, CYA, and bleach bucket. Mixed.

Finished all this after midnight so I didn't wait 2 more hours to test. Actually waited about 5.5 hours.

Bucket Results: pH 7.5-7.6, FC 1.5, TC 1.5, CC 0! (Does this confirm the theory?) I added about 1/2 gal of bleach to pool after the test. CAT controlled reading showed pH 7.8 and ORP down to 650 (interesting).

I vigorously stirred the bucket with my face at the water level and I was able to make myself cough. Can't honestly say if it was the odor, a mental thing or a near drowning incident.

Several questions come to mind:

1. Where to go from here? Isolate my spa and run the test on a bigger scale. Coughing is worse with jets running, but we get it with vigorous splashing.

2. Ventilation: the huge industrial fan that is part of the ventilation system clears (and controls moisture) the room very well. I have the humidity control set at 30% so the fan keeps running. Is it enough? Should I have additional fans blowing at my aeration points?

3. Should I run the bucket test with just super shocking in case this is regular CC and NOT the nitrogen based CC. How can you tell the difference?

4. This odor has been around almost since day one. Why? I didn't test high CC until late summer early fall. Most of the summer I had trouble regulating all the chemicals and the FC chlorine was mostly high (like 10 ppm).

I guess I will think of other question. Many thanks for your thoughts and help!!

Jeff

 

[chem geek]

Jeff,

Thanks so much for doing the experiment. Here are my comments.

You say that the pre-bucket pool reading had a CYA possibly near 30 because the black dot disappeared ("lost black dot") when the tube was filled, is that right? That doesn't make sense unless you ever added CYA or used Trichlor tabs/pucks or Dichlor powder in your pool -- did you ever do that? Or did you mean that you filled the tube and could still see the black dot the entire time and that the solution of CYA reagent plus pool water was clear? Your signature says that you used to have a puck chlorinator so perhaps that's where the CYA came from, is that right?

Did you have a second bucket of pool water where you did not add chemicals but did the same sort of mixing as you did with the first bucket? The purpose of the second bucket was as a control to simulate the mixing/aeration without the chemical addition. Otherwise, we can't really know if maybe the CC dropped due to the mixing/aeration rather than the chemicals.

1. Yes, we could isolate the spa and repeat the experiment there, but please answer the questions above first.

2. Though increasing ventilation, including how long the cover is open, is one approach, lowering the amount of nitrogen trichloride in the first place would be better. So depending on your CYA answer for your pool, we can go from there.

3. You are correct that you could just do a bucket test without the added CYA or ammonia and just shock with higher FC, BUT only if you already have some CYA in the water. If you don't, then add some CYA and shock with higher FC (perhaps 10-15 ppm). If the CC goes away, then it's more likely to have been monochloramine instead of nitrogen trichloride. However, given your difficulty getting rid of it in the pool with either chlorine shocking or MPS non-chlorine shocking, I think it's more likely to be some sort of persistent CC and given that ammonia+chlorine got rid of it, it's more likely to be nitrogen trichloride (the only thing inconsistent here is that if there were CYA already in the pool water then you shouldn't have built up so much nitrogen trichloride in the first place).

4. Nitrogen trichloride is VERY volatile and VERY odorous and irritating. It takes only a very small amount of even 0.02 ppm (20 ppb) to be detectable and though in theory this could measure as 0.06 ppm CC in that test which is below the 0.2 ppm threshold of the test, it's not certain that it does in fact reliably get measured in the CC test. Monochloramine and dichloramine are known to get measured as CC, but nitrogen trichloride is not as certain (info from Hach, but no reason given).

The fact that your FC levels were high was probably a large part of the problem. This would be especially true if you didn't have CYA or if your CYA was very low (< 20 ppm) in the water or if your pH got low. A combination of high hypochlorous acid concentration and low pH produces lots and lots of nitrogen trichloride and is definitely something to avoid. I suspect that though aeration and ventilation has been removing the nitrogen trichloride, the high FC level with low or no CYA has been producing it. With the cover on most of the time, you haven't removed it as fast as it was created so it built up.

One thing that doesn't make sense is that the nitrogen trichloride wouldn't keep building up if there was normal introduction of additional urea from bather sweat/urine into the pool. It would get to some steady-state level where it's breakdown rate (mostly from oxidation from dichloramine) would equal the introduction/creation rate and even in bad situations this would only be measured as perhaps 0.3 to 0.6 ppm CC unless the pH were significantly lower. A higher CC during and within a few hours of swimming would be normal when there's CYA and that would mostly be monochloramine, but it will mostly go away before the next day even with the pool covered. There's probably something wrong with the model. Anyway, your results getting to 0 CC were good -- we just have to reproduce this on a larger scale with the spa to confirm it.

Richard

 

[jcichocki]

When the pool was built it included a "puck" chlorinator, in addition they added a load of CYA during the initial start-up. I forget how high the CYA (somewhere around 100) was when I figured out they had screwed up.

I have since removed the chlorinator, drained half the pool and refilled it. I added the bleach system after finding this web site. So, yes, there is some CYA still present. It is below 30. I lose the black dot when there is literally a water dome on the tube before the dot disappeared.

The second bucket numbers were unchanged from the pre-test numbers. I stirred the buckets as you instructed but I did not spend more than 15 min stirring anything (except that saddistic CYA). Maybe I should re-run the test with more aggressive stirring.

At this point with this coughing problem, my wife would probably donors here expensive kitchen mixer. I am willing to try whatever your next thoughts.

Thanks. Jeff

 

[chem geek]

I wouldn't bother redoing the second bucket test. So long as you stirred it and left it open for the same number of hours, that's good enough. You basically proved that intentionally making some monochloramine (and dichloramine) by adding ammonia will work to remove whatever is getting measured as CC, most likely nitrogen trichloride though I still don't understand why it's so high. At this point, whatever works is reasonable.

So I'm going to figure that your CYA is probably between 25 and 30 ppm since it's a logarithmic scale as you can see on the tube. So having the FC at 10 ppm with the CYA in that range is definitely higher than you would normally want, especially for an extended period of time, and this would make more nitrogen trichloride than if the FC was more normal at around 2-3 ppm. Given your automatic dosing system, large pool, and relatively low bather load, I would think you would be able to keep the FC at 2 ppm fairly reliably which should help prevent this problem in the future. It should technically have the level of irritating nitrogen chloride be about 5 times lower than it is now. It would still be a good idea to air out the pool more in the future, but that's something where you can monitor the CC over time and just air it out longer if you start measuring CC.

So back to our next step which is trying this on a larger body of water, namely the spa. Can you estimate the volume of the spa by itself? That's probably hard to do, but if you look online at typical spa sizes you'll see that 350 gallons is pretty common. Of course, yours may be bigger since your pool is rather large and it's built-in like the pool and not a separately purchased spa. Perhaps it's 500 to 750 gallons, if it's big. We don't have to be exact, but I'd like to be roughly in the ballpark. Let me know that number as well as its current FC and CC readings (I'll assume the CYA hasn't changed) and I'll give you a recipe to follow. If you can keep your spa less heated and at roughly the temperature of the pool, that would be better since we really want to simulate what would happen in the pool.

If, and only if, we have success in the spa, then we'll do something for the pool. You'll have to get a stronger source of ammonia. See if a local drug store has ammonia (aka ammonium hydroxide) which may be at 27% strength. If you can't find any, then at least see if you can get 10% ammonia at some grocery/hardware store. We'll probably keep the CYA as is and we'll see about the FC.

Richard

 

[jcichocki]

I am away from home and having some trouble estimating the spa volume. As I recall, the spa is approximately 5 x 7 feet. Maybe 3 feet deep (standard depth?). There is simple bench around the entire perimeter of the spa. There are also two small steps, one above the bench and one below coming out of the corner.

Hopefully this will give you some idea of volume. Otherwise I will get some calculations on Monday night.

Jeff

 

[chem geek]

I'll bet the depth is closer to 4 feet otherwise sitting on a bench would have you mostly out of the tub since the bench is probably 3 feet below the surface and an additional 1 foot to the bottom. With the bench taking up some space, let's just figure around 900 gallons. It's probably somewhere between 750 and 1000 gallons in any event.

So take some measurements of the FC and CC of the spa. If it's consistent with your earlier measurements in the pool, then it will be 2-3 ppm FC with 1.5-2 ppm CC. I'll assume that the 2 ppm CC is nitrogen trichloride (even though I don't know how it could get so high) so means there's really 0.66 ppm since there are three chlorine in that chemical. So we want 0.66 ppm of ammonia in chlorine units and that's about 0.13 ppm in Nitrogen units which is close to ammonia itself. In the bucket experiment I didn't take into account the factor of 3 so we'll try this in the spa with the lower amount of ammonia -- worst case, we'll have some CC leftover and can add more ammonia to get rid of it.

You'll want the FC level in the spa to be at least 2 ppm, but not more than 4 ppm. I'll assume there's around 25-30 ppm CYA just as there was in the pool water you measured earlier.

So, assuming you can get 10% ammonia solution, in 900 gallons this would be ((0.13 * 900 / 1,000,000) / 10%) * 128 *6 = 0.9 teaspoons of ammonia. So if your ammonia is weaker, you can just scale up accordingly. For the spa test it's not a big deal and even for your pool it's probably not a big deal to use weak ammonia either (we're only talking about a cups worth of the weak stuff). I think it best to take a bucket of tap water and add ammonia to it and then slowly add this diluted mixture to the spa with the circulation pump running.

Let us know how this works out in the spa which, of course, needs to be isolated and not circulating with the pool water during this experiment.

Richard

 

[jcichocki]

For the sake of speed, I will use the 2.5 percent ammonia that I already have. I re-did the math, is it correct that I only need 3.6 teaspoons to treat the entire spa?

I will treat and report back in a few hours (with fingers crossed).

Thanks again.

 

[chem geek]

For the sake of speed, I will use the 2.5 percent ammonia that I already have. I re-did the math, is it correct that I only need 3.6 teaspoons to treat the entire spa?

I will treat and report back in a few hours (with fingers crossed).

Thanks again.

Yup. That's correct. As I said, it might not be enough, but in theory it should be and I'd like to validate that. So try that amount and report back what happens after giving it some time. I assume you've got some FC in the water (at least 2, but not more than 4).