SLAMing Hot Tub with Ozonator

After some hot tub rash, I've been SLAMing my covered hot tub (using the 13ppm FC recommended in the PoolMath app). With 33ppm CYA, I've been raising the FC to 13 ppm 2-4 times throughout the day, testing at the end of the daylight (about 4pm) and then testing again the next morning (about 9am). Based on the Pool School article, I've gotten the CC down to under 0.5 (good), but it recommends an overnight FC loss of 1ppm or less (the water has been clear the whole time). The last two mornings the FC level has gone from 13ppm to 7ppm. But when I did a forum search I saw @chem geek mention that ozonators can degrade FC so that we should expect something like a 50% decline in FC in a 24 hr period even without the need for disinfecting or oxidation. My hot tub filter system runs 8am-noon each day (which is when the ozonator is active), so by 9am it will have been ozonated for an hour. I can see several options here:
1) Turn off the ozonator for one day to get a clean reading and watch for a 1ppm FC overnight loss
2) Change the overnight FC loss threshold for this situation to... ...something?
3) Have three days in a row of retaining 7 of my 13 ppm of chlorine and call it good enough
4) Something else

Any advice for hot tub SLAMing with ozone?
 

JoyfulNoise

TFP Expert
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May 23, 2015
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Tucson, AZ
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We don’t typically recommending SLAM’ing a hot tub, it’s just not worth it. If you are getting hot tub rash, that’s from pseudomonas bacteria and you likely need to do a purge of your tubs plumbing. We recommend you use Ahh-some to purge your tub (with chlorine added) and then dump the water. After the tub has been cleaned out and refilled, shock the water, rebalance the water, and then run as normal.

If you are not using bromine in the tub, then the ozonator isn’t really doing you much good other than eating up all your chlorine. I would suggest you turn off the ozonator if you are sanitizing with chlorine.
 

RDspaguy

In The Industry
Mar 21, 2020
1,219
Cabool, Mo
@JoyfulNoise is a very knowledgeable and clearly intelligent individual, and I agree with most of what he says. But I AM a fan of ozone in my chlorine spa, precisely BECAUSE it eats up the chlorine. I don't like a high chlorine level when I use my tub, but still need to get enough in there to deal with the contaminants introduced during use. I nail it (yes, that's a technical term ;) ) after each use and rely on my ozone to get rid of the cc and any extra fc before I use it again the next day. With my cover on some 22+ hours a day, I have little risk of any new contaminants entering the water, so a low chlorine level does not present the issues it would in an open pool or spa. I also use silver ion (nature2) as an additional buffer against any new contaminants. I know it's not popular here, but it is what I have done for many years and it works great for me.
But there is nothing wrong with going old-school and using sanitizer alone, whether chlorine or bromine. Though tablet floaters are a bad idea in my opinion. In a privately owned spa, it's your choice. In a public spa, neither ozone nor silver ion makes a lick of difference in the required sanitizer levels, so would be worse than a waste, since ozone (as you have seen) depletes chlorine levels.
Trying to maintain a chlorine residual with ozone is like trying to maintain one in a pool in Arizona with 0 cya, or suntanning in coveralls, or eating BBQ ribs with a covid mask on. 🤪 It just isn't going to go well... :ROFLMAO:
I'd embrace it or get rid of it. The air injection is not going to be helpful with your ph, unless you use dichlor and drain frequently, so if you don't appreciate what ozone is doing for you then it's best to remove or plug off the injector as well as disconnect the ozonator.
 
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Turn off the ozonator.

What water temp do you have the tub set to during the SLAM Process?
I'm guessing between your and @JoyfulNoise 's response, you mean to turn if off for good and not as a temporary measure.

I'm keeping the hot tub at 100°F.

@JoyfulNoise, I see your point. I'm trying to conserve water on account of it being rare here, so I thought I'd give the SLAM a try, but if it doesn't work, then I guess I can run down the chlorine and drain it to the swale in our yard to bank it in the soil. It does have some bromates, but they should be rare enough to not impact the roots.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
24,942
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
If you want to continue the SLAM Process I would turn off the ozonator and lower the water temperature. No reason to maintain a water temperature during the SLAM Process and the higher water temperature also consumes chlorine.

Once you get your water reset you can try different spa care methods and see what works best for your setup.
 

cowboycasey

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Jul 3, 2013
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Southern OK
I am partially with @RDspaguy, when I had my hot tub I also ran chlorine with ozone but I added in a salt water generator.. it would keep the FC around 4 to 5 at all times and would fall to 1 after a soak... I used my tub 5 to 7 days a week so it worked for me... I would also change the water and purge with ahhsome every 6 months just because.... :)
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,743
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Let me elaborate more on my position when it comes to ozone (supplemental oxidizer) and chlorine (primary oxidizer and and sanitizer) in a hot tub. I have no dog in this fight so I really don't care much either way what people choose to do, but there are details here worth discussing and acknowledging so that users can make informed decisions.

The first point is this - chemistry in a recreational water body like a hot tub is very complicated and does not lend itself well to simplifications. This is true in pools as well but hot tubs are doubly more complex because they are very small water volumes with very high bather loads, they are constantly heated to high temperatures, and the human body emits and sheds all kinds of nasty chemical compounds. If anyone has every given a child (or two or three or four) a bath, one notices right away that the pristine water the tub was filled with quickly becomes a cloudy and smelly soup of human waste. Hot tubs are only a bit bigger and typically hold multiple human bodies at perspiration producing temperatures for soak times much longer than the typical bath. This loads the water up with salt, urine (urea), creatinine, oils, proteins and, in some cases, beer (both virgin and .... processed, shall we say).

The second point - chlorine and ozone are both powerful oxidizers and sanitizers (although one doesn't typically use ozone for sanitation). They not only react with one another (neutralizing each other) but they also attack organic compounds in the water. These organic + oxidizer reactions are very complicated and there are cross reactions between the two oxidizers. You can't just simply say that because one oxidizer does one thing, the other oxidizer will sit back and wait....reactions happen simultaneously and with varying complexity. Most of these reactions will result in what you want them to do - oxidize complex, organic bather waste into simpler compounds. However, some of these smaller, simpler compounds will then go on to react with the chlorine further potentially leading to end-products (trihalomethane and disinfection by-products) that can no longer be oxidized and are toxic in nature.

The third point - not all combined chlorine (CC) compounds are created equal and some are definitely "more equal than others" (that's an Animal Farm reference for anyone who ever read the book...). Simple, inorganic CC compounds like monochloramine and dichloramine can be further oxidized by chlorine and ozone to chloride salts, nitrogen gas and nitrates. However, organic chloramine compounds, like chloroform and chlorourea, can not be broken down much further by chlorine (even at shock levels) and ozone has trouble with more complex organic chloramines. This is subject of "breakpoint chlorination" and what gives rise to the total chlorine versus free chlorine curve where one sees that the TC stops rising and eventually falls when the FC gets high enough. But there is sometimes a "floor value" of TC which increasing FC never reduces and that is the non-reactive chloramines that are formed. Ozone can reduce that floor value a little bit but it rarely can bring the TC down to zero at reasonable ozone levels.

Final point - hot tub ozonators are garbage and the industry knows it. Most of the ozone hardware slapped onto a hot tub are toys - their input gas is air (not pure oxygen) and they often employ a UV light source to generate the ozone or the use a cheap corona discharge (CD) tube. These units barely produce adequate or consistent ozone levels and, after about a year, they no longer output ozone at all. Real, commercial-grade ozone injectors use either pure oxygen or dried air (water vapor in air kills ozone output) to generate the ozone and the CD tubes used are typically field-replaceable because they wear out and need to be changed on a regular basis.

Now, if you plan to run a hot tub using bromine as your sanitizer, then an ozone generator is a good idea because ozone regenerates spent bromine (bromide) back into sanitizing bromine and bromamine compounds don't have the same cross reactions as chlorinamine compounds do. You still have to contend with the equipment issues of replacing the ozonator when it fails.

If you're running a tub with chlorine, simplicity would be my choice. Will ozone probably help out in a small, residential tub, sure. But it seems like one can get the same benefit by simply running a drape-over SWG in the tub. Chlorine works fine as an oxidizer and sanitizer and an SWG tends to generate some free radicals as well as chlorine so there is a good mix of powerful oxidizers there. Adding more oxidizers in the form of ozone just simply seems unnecessary to me and, for the most part, all it will do is create greater chlorine demand. Since there's no way to measure ozone residuals in water (they'd be very low anyway since ozone does not dissolve in water much), one is basically left to guess if it's working or not. This is why I'd rather just see the ozone turned off and avoid any unnecessary complexity and guess work. I can easily measure FC and CC and, if CC's build up, then simply dump the tub and start over. Even here in Arizona where water is more expensive than electricity or cable TV, dumping a hot tub every few months is really nothing at all....people waste more money irrigating plants that don't belong here or trying to maintain lawns in a climate not suited for grass.

Just my 2 cent opinion for what it is worth....
 
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cowboycasey

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Well that makes sense now, The first year I had my tub I was using bromine and it worked, the next year it did not work and that is when I changed to chlorine and then to SWG on year 3... The SWG worked great but I had no idea the Ozone had probably stopped working 2 years before :) :unsure:
 

RDspaguy

In The Industry
Mar 21, 2020
1,219
Cabool, Mo
Ozone generators for spas are rated in hours, so the actual timeframe that they last is dependent on how often they run and which unit you have. Those with 24/7 ozone injection (my preference) will burn out much quicker than those that only run during filtration cycles.
Some ozonators have replaceable tubes, cartridges or bulbs, and some do not. There are also various output levels, and the ozonator output and mazzei injector feed rate are linked. Replacing an old low output bulb ozone with a new high output CD and not changing the injector can cause a number of destructive issues.
A dealer I used to do some work for about 7 years ago had an issue with new tubs developing excessive yellowish foam (and I mean 2-3 ft above water level), clogged filters, and heating issues. In troubleshooting this I discovered that the ozone injection tubing was filled with sticky, stinky yellow goo that would curl your nose hair if you smell it up close. Still not sure what it was, but it was caused by a new high output CD ozonator being installed on the old style mazzei. We replaced mazzei injectors and tubing and the troubles stopped. Notified the factory and no more troubles. Best theory I heard was nitric acid buildup from ozone was melting the injection tubing and depositing the resulting goo in the tub via the mazzei. Again, I am not sure if that is correct. As a repairman, I didn't much care as long as the problem was fixed. ;)
But I can appreciate joyfuls views. It is an unmeasureable variable in a complex equation. I have just been using it successfully for so long I can't imagine not using it. But you do need to watch for it to fail. I usually notice the change in my water chemistry, like @cowboycasey , namely my chlorine residual not rapidly depleting anymore.
 

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