Problems with residual CC

[ducru]

I have another Newbie question and appreciate everyone's patience while I work through issues on how to manage my spa's water.  First of all, I sanitize with lithium. Last weekend, I noticed that I had a fairly high level of CC in my spa (+ - 3 PPM). I immediately shocked it by using a pouch of Activ'clear, which is a non-chlorine based shocking agent sold by one of the major Canadian Pool/spa retailers (it contains peroxy monosulfuric acid, monopotassium salt  and potassium bisulfate, among other things).  The next day, there was still 2 PPM of CC, so I shocked it with a product called OXY (which, I believe, is the same as the other product, except that it is made for pools and is more concentrated).  This treatment also left residual CC, so the next evening I added 4 tbsp of Lithium (my spa holds 340 gallons), which I now know, simply superchlorinated the spa and probably actually added more CC to it). In any case, the hot tub has started emitting a sweet chemical smell (not unlike antifreeze), which will not go away. Yesterday, I emptied 1/3 of the water and re-filled, but the smell is still there and so is the CC. I've been leaving the cover off as much as possible for the last 2-3 days, in hopes that this might help, but the smell lingers. On the other hand,  the water is very clear.  Does anyone know what I should do at this point.  Should I shock it again, and if so, with what ?  How often can one shock a spa ? Also, while I'm working to get rid of the CC, can I soak in the spa ?

[kporter]

I would stay out of the hot tub for a few days while you get your chlorine situation figured out. Soaking in the hot tub is only going to make the issue worse and may be uncomfortable for you, potentially harmful. When you are shocking with lithium chlorine are you hitting break point chlorination - 10 ppm? If you are under shocking you are just adding to the problem.

Porter

[ducru]

When I did try to shock with chlorine, I don't think I added enough (so I found out later).  That's why I'm wondering if I should shock again and, if so, with chlorine or with non-chlorine agent ? From what I've been able to gather, if my CC is at 2 PPM, I should be raising the chlorine to 20 ppm (10x) ?  That's a lot of chlorine !

[chem geek]

Non-chlorine shock (MPS) will measure as CC in DPD test kits (and as FC in FAS-DPD test kits if any FC is present).

[ducru]

Hi chem geek.
I have the Taylor K-2006 test kit (therefore, FAS-DPD, I believe).  Right now(yestersday) it is showing 1.00 PPM of FC and 2.00 PPM of CC. My last shocking of the water was on Sunday, when I used the OXY (MPS). On Monday I used 60 gr. (4 tbs) of lithium and yestersday I replaced 35% or so of the water and then added 1 tbs of lithium.  If I'm using the K-2006, are you saying that I could actually have more CC, if the measured FC is actually a false result ?  Could I actually have no FC and 3 PPM of CC ?  On the other hand, if I measured on Tuesday evening (yesterday), I'm assuming that Sunday's MPS shocking has dissipated and would no longer show up in the testing, would it ?  Bottom line: Where do I go from here ?  Can I soak in the spa in the meantime and how do I go about getting rid of the CC. Shock with lithium, shock with MPS or simply ditch the water and start over ?  If I should shock it again, how much do I need ? My hot tub holds 350 gallons. Thanks for your assistance.

[chem geek]

So that CC is probably real and not just MPS since the MPS would show up as FC since it would react with the FAS-DPD drops.  You could have 2 ppm real CC and 1 ppm of MPS and no real FC.  The MPS should dissipate if there is something for it to oxidize -- it doesn't outgas like chlorine can do with hot water and even faster with aeration.

If the spa doesn't smell bad, then the CC may be something innocuous like chlorourea.  You can try shocking with chlorine -- which type is up to you (lithium hypochlorite is fine to use, but is expensive).  In the meantime or in between shocking you can soak if you want to.  You can use PoolMath to calculate how much to add.  10 ppm FC in 350 gallons would be 1.3 ounces of lithium hypochlorite.

[ducru]

I ended up shocking the spa last night with a good 2.25-2.50 ounces (4.25 tbs) of lithium, and it does seem to smell a little better this morning.  When I checked the chlorine levels this morning, the FC is up at 10.5 ppm, and the CC is down around .6 ppm; better, but the CC is still hanging around.  I will leave the spa top open for a portion of the day, in order to let the chlorine dissipate and I will re-check the levels later today.  Is shocking the only way to rid the spa of CC, or can it work it's way out of the spa on its own (either with the help of present FC, other chemicals or by just airing the spa out) ? Should I keep shocking it until the CC falls to 0 ?  How often can one shock their hot tub ?

As for the smell, it isn't a foul or acrid type of smell, but rather an almost ''sweet'' smell of chemicals, mixing with chlorine. Could it be caused by an accumulation of all the PH reducing agents, alkalinity and hardness increasing compounds that have been added over the past 3-4 weeks ? Another possibility I was entertaining is that the hot tub is located close to a bunch of maple trees. At this time of the year in eastern Canada, these trees are dropping their seeds, which fall to the ground in 3'' pods we call ''hellicopters'', from the way they twirl while falling.  I try to keep/fish them out whenever or as soon as possible, but I assume they are adding organic materials to the spa which is then being attacked by the FC, and therefore creating more CC.  Does this make any sense ?  If so, it should be quite the balancing act between airing out the spa regularly and fighting to keep the falling pods and, soon to be, leaves from falling into the spa. Any further thoughts ?

[chem geek]

If the CC is volatile, then a combination of shocking and aeration can remove it.  If it's not volatile and if it's slow to oxidize fully from chlorine, then physical removal (i.e. water change) is the way to get rid of it.  There are more advanced coagulant/flocculant products used commercially (e.g. PRS 2-stage system), but that's overkill for a small residential spa.

[ducru]

I will take a look at it and if it seems to want to stay, I will simply change the water.  Thanks for your input.