CC level

[nicpppardo]

Hello!

I have had my hot tub going for almost a week now, and I have a question about the chlorine levels.

My hot tub this morning was at FC 5.5ppm CC: 0. I went in the hot tub and measured the chlorine again when I got out, just to get a feel for what happens. When I got out, FC was at 4 and CC was at 0. Tonight, I wanted to go in again. I tests the levels first and they were FC: 4 and CC: 1.

My question is- my FC level never dropped too low. How did I end up with CC at 1? I just raised it to a shock level of 13 ppm, but I'm just not sure what happened. I'm assuming I should always shock if any CC shows up, but especially above 0.5.

Hot tub: 375 gallons
pH 7.2
TA: 60
CYA: ~30
Borates: 50

Thank you!


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[chem geek]

That is not how you do this with a hot tub. You normally don't want to soak with a higher chlorine level because with the hot water and aeration you will smell more chlorine and chloramines. If you are soaking with strangers or in a commercial/public hot tub then a higher FC is OK, but most people prefer to start their soak with 1-2 ppm FC. You then add sufficient oxidizer after your soak to oxidize the bather waste. CC is normal at that time because the bather load is high in a small volume of water but over the hours after your dose after your soak the CC should go away.

Usually the bather waste is oxidized within 24 hours and often within 12 hours, but perhaps in your case it is taking longer. Is your hot tub water hot (near 104ºF)? How long were you in the hot tub and was it hot (104ºF)? Every person-hour in a hot tub with no ozonator would usually need around 3-1/2 teaspoons of Dichlor or 3-1/2 fluid ounces of 8.25% bleach or 7 teaspoons of non-chlorine shock (43% MPS) to oxidize bather waste. In 375 gallons this would be 6.5 ppm FC.

You normally don't need to shock because usually the CC is dealt with by the time of your next soak, but obviously that didn't happen in your case perhaps because your soaks were too close in time and perhaps the water wasn't warm enough.

 

[nicpppardo]

Your write up is helping this make sense! When I first went into the hot tub, it was around 100 degrees and I was in for about 30 minutes.

So if most people like to bathe around 1-2 ppm (which I can understand- the smell of chlorine is definitely there around 5ppm), how do I have 4 people in the tub at once and not cause trouble? Or even 2?

When my family gets back, let's say we'll realistically have 2 people per hour each day in the tub (my parents live in theirs in Florida, and we get "colder" weather here in SoCal so I think this is my reality!) Is it ok to have the tub at 2ppm when 2 people soak for one hour? And then when they leave after that hour, would I put in 7 oz of bleach (8.25%)?

Sorry to play a bunch of what ifs, but I have one more round- at night, I'm sure I will use it a lot. This means that within a 12-18 hr period, we'll have a couple rounds of people in and out. Would the tub still be comfortable for me to get in let's say 6 hours after my parents used it and added the bleach when they exited?

I'm just trying to figure out a good routine so we can all enjoy! I very much appreciate your help!


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[chem geek]

Using the tub once a day should be easy and work out well, but using it twice a day would likely have you with more bather waste not fully oxidized by the time of your next soak. So you can still get into a routine where you add enough oxidizer after each soak to have at least 1-2 ppm FC for the start of your next soak, but if you were going to skip a soak you'd want to add more because you don't want the chlorine to get to zero.

As for what to do when you have more people in the tub, most residential spa owners just have the lower chlorine level run out during their soak where it mostly produces monochloramine and while that still inhibits bacterial growth it isn't a fast kill for person-to-person transmission of disease. So this isn't something for commercial/public pools to do but whether you want a fast pathogen kill during such soaks is up to you. In one hour you aren't going to get uncontrolled bacterial growth so the question is whether you want to quickly kill anything shed from one person that could reach another (bacteria, viruses). If it's your own family, then odds are you are getting exposed to their viruses anyway. So this is really a personal choice. For sure after a soak you want to blast with chlorine to kill off what is there that may not already be killed and you want to oxidize the bather waste.

For consistently higher bather load situations such as what you are describing, you'd be better off with an ozonator as that will handle this bather waste. Ozone also depletes chlorine, but when you soak every day or twice a day then the ozone lowers the amount of chlorine you need to add after each soak by at least half. So ozone is only a problem with chlorine when you don't use the spa frequently. It doesn't work well for those just using the spa on weekends, for example, because it more than doubles chlorine demand in between soaks so during the week one would have to add chlorine nearly every day.

So you should try experimenting with how much chlorine you need to add after each soak and see how long it lasts given the bather load. While you can start off with the rule-of-thumb I gave, you should adjust to your specific situation.

 

[nicpppardo]

Ok this is all making sense. It'll definitely take some playing around to figure out how to use the tub a couple of separate times, but now I do see best practices that'll give me the best shot. One last question, and I apologize if this was answered and I have missed it. Considering I went a little crazy on the chlorine (still hanging around 9, so just waiting for it to go down), I do not understand how I have any CC. Right now I have 1 CC still, and I haven't been in the tub in over 24 hrs. How can that be considering my high levels of FC? Thank you!


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[chem geek]

Some CC is more persistent, particularly chlorine combined with urea. The easiest way to handle it is to expose the water to sunlight. Usually in hot spas it goes away, but may take 24 hours instead of just 12 so with your higher bather load it may build up some. The good news is that chlorourea is relatively innocuous itself. If you don't notice a "bad chlorine smell" (not a bleach-like smell) then the CC is likely not a problem. This is again a situation where an ozonator would help or even a UV system.

Technically, a SLAM or significantly elevated FC level relative to CYA would make the CC go away faster, but that can also create smellier by-products so it may not be worth it. Higher active chlorine levels produce more volatile and irritating nitrogen trichloride when oxidizing ammonia and the same may be true for oxidizing urea as well.

 

[nicpppardo]

Thank you! I called the hot tub company and hidden in the specs was the idea that I do have a ozonator. I just got to this today, so tomorrow I am going to try leaving the top off to get some sun light in there. I haven't been in the tub since this post and now my CC is up to 1.5, while my FC has been a bit in the higher side. Man oh man, hot tubs are harder than pools! Haha


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[chem geek]

I know you said in another thread that you bought Ahh-Some but didn't use it because you are under water restrictions so wanted to wait before changing the water. Just remember that new spas have greases/oils leftover and can also have biofilms from wet testing so the CC might be from that in which case the sunlight will only help some but what is really needed is to use Ahh-Some. You'd have to change your water after using it, but you will be amazed at how much junk comes out of the spa. So if the sunlight doesn't help enough or if the water just gets too yucky, I'd suggest using the Ahh-Some and changing the water.

Usually anyone getting a new spa should REALLY fill, use Ahh-Some, then drain and refill. That's the best way to start out in good shape. What you have is not a disaster, but the combination of not doing an initial purge along with your high bather load is really putting a strain on your hot tub water.

 

[nicpppardo]

That makes a lot of sense. I finally got the CC down to 0.5. However, I do think it needs a round of ahh-some like you said. I'm going to keep doing my testing daily and try to get to September before emptying and refilling so at least there is a month between each fill. Thank you for all of the help!


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