Combined chlorine = 0 but hot tub still has bleach smell

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watson524

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Nov 13, 2014
182
Lake Ariel, PA
Hi all,

Quick question re: CC and smell. As I understand it, the chlorine smell is caused by combined chlorines. We switched over to bleach recently and keep it at about 8 - 10ppm due to our high CYA level and no time to dump just yet. When we lift the cover, we can smell the bleach smell, not overpowering like a public hot tub/pool, but it's definitely there. In the water, I scoop some up and sniff and really don't smell it. Our CC as of our most recent test yesterday was 0 (when I did the FC test and then added the 5 drops of R-0003 (Taylor kit), we didn't have any pink at all. In past weeks it's been 0.2 since one drop in a 10ml sample turned it from the light pink back to clear again.

If this smell we're smelling normal?

thanks!
 
Ok that's weird, thought it was in the signature... 500 gallon Jacuzzi J-385. Got it new in late December 2014. Still on the first water fill. Had been using MPS/mix with Nature2, water went cloudy and nice folks here walked me through switching to 8.25% bleach (didn't realize that as CYA level went up, FC ppm needed to raise, hence cloudy water and shocked it to resolve that). That was all over a month ago. Water went back to crystal clear and the bleach method is pretty easy to deal with tho I'm still in testing each day mode in order to make sure I know normal daily FC loss with no bather load (about 4.5 - 5ppm) and also the per person hour FC loss (about 5.5ppm). Given our CYA level, 90, we keep the FC between 7 and 10ppm.

As of yesterday's weekly maintenance (filter rinse, not a change this week) and testing:
pH: 7.2
FC: 8.0
CC: 0.0
Alk: 80
CH: 110

Thanks!
 
yep, 500 gallon will cost you about a dollar to change out that water :) I change mine every 6 months just cause....
 
Bummer, sorry, us too actually. That is lots of work!
We're down to 98 in our tub.

Ok, how about adding borates?
put 28oz of 20 team mule borax and 14oz of 31.45% muriatic acid in your tub. That will help.
 
Are our TA and pH at ok levels to do that or should our TA be a bit lower yet? It looks like it would be a net loss of 0.6 on the pH to do that (TA would be a net 0 apparently) so I almost think my pH should be higher before I start the Borax + MA.
 

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Hey, you're pretty handy with that poolmath! Yes, would need to tweak ph. Don't see your TA level up there.

Did the checkbox for show signature get unchecked? Lower left.
 
If the smell is like a bleach smell and not a bad pool smell then it probably is chlorine because 1) hot water outgases chlorine faster and 2) the hypochlorous acid gas (which is mostly what it is, not chlorine gas itself) will build up under the cover so when you remove the cover you are getting the most concentrated whiff of it. That's why you don't notice it once in the water.

The chlorine/CYA relationship is different at higher temperature so you probably don't need to have the FC as high as you have it even with the CYA being high -- at least if you keep the tub hot. Also, one generally starts a soak with a lower FC level, usually in the 1-2 ppm range, but that's with a "normal" CYA level of around 30-40 ppm.
 
TA is 80 (sorry, I wrote it as Alk above)

Looks like I could just add about 7.5oz more Borax once I get the Borates to 50ppm to raise the pH from the (assumed, I'd test first) 6.6 back up to 7.4

Definitely not a bad pool smell, it's like a load of white laundry after it's done the spin cycle. (i.e. not the strong initial bleach, just the faint smell at the end of the load).

We've been working to keep it so that 24hr after the soak, we're still in the 8 - 10ppm range. We happen to soak about 24 hours from the last dose time so even when we're getting in, it's about 8 - 10ppm. Tho it's good to know if it was a bit lower than that when we got in, it's ok.
 
Ah ok, didn't realize that the CYA chart was more for pools and not the high temp of the hot tub. Since we lose about 5ppm in 24 hours with no bather load and about 5 - 5.5ppm / person hour I've been targeting 10 and then adding 10ppm so I'll see what happens if I target 4 - 5ppm at soak and add the 10ppm post soak.
 
Losing 5 ppm FC in 24 hours with no bather load is quite high. Do you have an ozonator?

What is the size of your spa? The 5 to 5.5 ppm FC per person-hour would be around 450-500 gallons if there was no ozonator but with an ozonator the chlorine usage would normally be lower since ozone oxidizes at least half of the bather waste before chlorine reacts with it.
 
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