Help With Chloramines

[mck75]

I’m a newbie to spas, but have been studying spaology on this forum. The information here is incredible. Just got our hot tub, a Marquis Rendezvous, a couple of weeks ago. It is a small tub and only holds about 150 gallons, but it is perfect.

I have been using chlorine in various forms and don’t seem to be able to get a handle on the combined chloramines thing. I can see the FC go up after dosing with chlorine and then go down after tubbing, but the CCs seem to be hanging out at around 2.0 no matter what I do. I read in another post about MPS causing a false reading and I have used MPS a couple of times, so I am not sure what my real CC level is, just kind of go by smell that combined chloramines are present. If I got the test kit for MPS, would I subtract that reading from the CC reading to get my true CC?

I used Dichlor initially and when the CYA level was 100, I tried Clorox, but it just didn’t keep the FC up more than a few hours. So I tried Lithium which seems to work okay, but does move the pH up a little. The tub has an ozonator and I added a mineral frog to provide some extra sanitation when the FC gets low.

Anyway I tried shocking and another time I tried adding MPS, but now I am not sure what my real CC is and what to do about it. Yesterday I added some DiChlor and ran the jets a lot while there was a little sunlight available and that made it smell good, but the next time I added chlorine to leave a residual FC, then I got the smell and a CC of 2.0 after 12 hours.

Any suggestions would be greatly appreciated.

Rebecca

[chem geek]

Rebecca,

Regardless of the source of chlorine you are using, it sounds to me like you aren't using enough so what is happening is that the ammonia/urea from sweat isn't getting fully oxidized. You either need to use a larger quantity of chlorine or you need to use a non-chlorine shock (MPS) to supplement. In a small volume of water such as yours, it still takes the same quantity (weight or volume) of oxidizer (chlorine or MPS) to get rid of ammonia/urea, but adding that amount in the water will initially make the equivalent FC to be much higher, at least briefly, and then it becomes CC and then over time that goes away IF enough chlorine or MPS is being used.

Can you tell me how long you soak per day and how much chlorine of each source (bleach, lithium hypochlorite, Dichlor) you added each day?

Richard

[mck75]

Thanks for getting back to me so quickly, I have been admiring your posts and was hoping you would reply.

As far as tub use, an average of 2 to 3 uses per day. I have been adding a teaspoon of DiChlor or a tablespoon of Lithium after tubbing and an equal dose in the morning or evening if the FC is less than 2 or 3.

It seems counterintuitive to add more chlorine when it already smells like chlorine, but I guess that is what I need to do. Last night I added 3 tablespoons of Lithium and couldn't check PH or chlorine a few hours later because everything just turned dark magenta. But by morning the FC was 7.5 and the CC was 2.0. But as I mentioned before, I added MPS a few days ago so I am not sure about the CC level. It did smell a little chloriney.

So I will try adding twice as much after tubbing and see if that helps. If I use MPS is there any way to test for CCs.?

Thanks, Rebecca

[chem geek]

Rebecca,

1 teaspoon of Dichlor would raise the FC in 150 gallons by 4.6 ppm (and the CYA by 4.2 ppm). A tablespoon of Lithium hypochlorite in 150 gallons would raise the FC by 8.7 ppm so these amounts aren't equivalent, just so you know (unless the Lithium wasn't around 35% available chlorine).

One thing you said didn't make sense to me. You said that you add more chlorine if the FC is less than 2 or 3, but are you saying that you are measuring both a non-zero FC AND 2.0 ppm CC during the same test? Are you using a FAS-DPD "count the drops until pink/red turns clear" test for FC and CC? Or are you using a DPD test where you compare the pink/red color intensity against a standard? Because you said everything just turned dark Magenta, it sounds like you are using a standard DPD chlorine test. How were you separately measuring FC and CC? With a DPD test, you first add the indicator and measure the color for the FC amount, then add another reagent and then measure again, but this gives the Total Chlorine amount, not the CC, so will always be greater than or equal to the FC amount. It is the difference between this second measurement and the first that is the CC amount, though in a DPD test it's not that accurate. So do you really have 2 ppm CC in that adding the extra reagent makes the DPD test get even darker?

Anyway, if it's one person using the spa for cumulatively one hour per day (does that sound right to you?), then that would roughly require the equivalent of 16 ppm FC in your small 150 ppm volume of water (it might be less if you sweat less). Yes, you read that correctly. Now there's no way we're going to want the chlorine to get that high unless we use a higher CYA level so it's probably better to use MPS to deal with oxidizing the organics. One person-hour would take a little more than one ounce volume (1.6 ounces weight) of non-chlorine shock (MPS). So if you added the Lithium twice a day, you were probably at the right amount, but if you just used the Dichlor, then it was probably too low.

Another possible issue is the CYA level which might be too high depending on how much Dichlor you've been using, and it sounds like it could have been a lot. If the CYA level is too high, then it will take too long for chlorine to oxidize ammonia/urea and instead it will get stuck at combined chlorine (monochloramine). So with a good test kit you can measure the CYA level.

As for chlorine smell, yes it's counterintuitive, but it's true. True chlorine doesn't smell very much and it smells more like diluted bleach as a clean or fresh smell. I suspect you are smelling chlorine combined with ammonia (monochloramine) which is much more volatile than chlorine and smells worse, more like the typical smell in many indoor pools.

So first, if you don't have a proper test kit such as the Taylor K-2006 or TF100, then get one. Second, if you have a good test kit, then try experimenting by increasing the chlorine dose to see if you no longer measure CC, but the trick is when to test for CC. You need to test quite a while after you've added the chlorine and before you get in to use the tub. If you find that adding more chlorine eventually reduces the CC, then we'll know that we guessed right about the problem. Then, the solution will probably be to use MPS as I described above, but that can get tricky as you might be sensitive to it and you use the tub frequently enough that it might not give enough time to prevent any residual from showing up, but I think some sort of balance between MPS and chlorine can be found that will work for you. The good news is that once you roughly figure out what's needed, it then becomes a very easy pattern or habit.

Richard

[mck75]

Thanks for your quick reply, Richard, I appreciate you sharing your expertise. I've observed that you act as a full time consultant working for free on this and other forums.

I am using the FAS-DPD test. An average reading (for me) would be FC 4.0 and CC 2.0 in the morning before tubbing or adding anything. (But could there be some MPS residual from yesterday?)

First I will try using more chlorine and hopefully that will do it. I was hoping not to have to use MPS regularly because it seems really harsh on my skin.

Thanks again for being so generous with your knowledge and taking the time to type long answers.

Rebecca

[chem geek]

Well, if you're using a FAS-DPD test and you're measuring 4 ppm FC, then the 2 ppm CC wouldn't be from have extra ammonia/urea around along with monochloramine so you probably are adding about enough chlorine. When you use MPS, then the CC could be some of it leftover, but it should go away through the next soak time unless you add more. So after eliminating MPS, that just leaves a couple of possibilities. One is that the CYA level is high so it takes too long to break down the monochloramine -- so test the CYA level. The other possibility is that you've got some persistent combined chlorine, but I find that unlikely unless you go into the tub with some lotion or makeup or other organics that may combine with chlorine but be hard to oxidize more fully.

Richard