chemical usage with an ozonator

Spa user

New member
Mar 24, 2021
2
Temple City, Calif
I just can't seem to figure it out. I now have an ozonator in my Hot Springs Spa. I understand that I can reduce my chemical usage quite a bit now. Before ozonator I was putting in one tablespoon of dichlor after each usage. Then MPS once a week. I've been told to follow the reading on my strips but if I cut back on my chemicals now won't that effect my strip readings? Lately I've been trying one tablespoon of MPS after use and one tablespoon of dichlor, once a week reversed from before but is that enough? The MPS doesn't even show a reading on my MPS strips. But if I put enough MPS in my spa to actually get a reading (or dichlor) then I'm defeating the purpose of my ozonator. I am very confused and any advise would be appreciated. Thank you.

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ajw22

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Jul 21, 2013
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Welcome to TFP.

From Ozone Systems - Further Reading

Ozone Systems in Spas​

The biggest plus with a functioning ozonator (not all work properly or put out enough ozone to work well) is that it will oxidize many contaminants in the water, but it's not fast as it takes time to get water circulated through the ozonator. Though spas circulate water faster than pools, it still takes 4.6 turnovers of the water to get 99% of the water through the ozonator and that's assuming no dead spots. You still need a residual sanitizer if you're going to prevent bacterial growth in the bulk pool water.[1]

The biggest minus with an ozonator is that it mostly injects air into the water and that aerates the water. If the ozonator is always on (and many are), this leads to a rise in pH if you use a hypochlorite source of chlorine. So many spa users use Dichlor which is acidic (when accounting for chlorine usage) and this helps maintain the pH, but has the CYA rise.

An ozonator probably makes more sense in a bromine spa than a chlorine spa as it can reactivate the bromide to bromine (though can create bromates -- so don't drink the water) and most bromine systems are net acidic so the pH will be more stable with the ozonator. As was pointed out, it is technically unnecessary if one maintains a residual sanitizer (chlorine, bromine, PHMB/biguanide/Baqua).

Just keep in mind that the sanitizer usage in a spa is MUCH higher than in a pool due to the lower water volume (higher bather load) and higher temperature that causes one to produce more sweat and causes chlorine to outgas more (especially with an ozonator).

If you use your hot tub a lot and keep it covered when not in use then an Ozonator can help, however if you only soak in it on the weekends, etc. then an Ozonator will actually consume more chlorine than the tub would use to oxidize bather waste if you did not have one. Also unlike Ozonators for pools, ones built for hot tubs are relatively cheap.
 
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RDspaguy

In The Industry
Mar 21, 2020
1,409
Cabool, Mo
I love ozone, and think it is better with chlorine and a waste with bromine. It reduces chlorine levels by burning off both cc and fc, but does not necessarily mean you use less to begin with. It just gets rid of the leftovers and byproducts.
Dichlor is almost half cya, and using it alone will cause high stabilizer levels quickly. You should switch to liquid chlorine (bleach) after cya reaches 30ppm.
I do not use mps. I add chlorine after each use and let the ozone take care of the cc, and the most of the residual fc. This gives me a "low chlorine" spa WHEN I USE IT, but does not mean I am using less chlorine.
In theory, ozone will oxidize bromide into bromine. But bromide and bromine are less reactive than chlorine, and from what I have gathered from those who use bromine, the ozone has no noticeable effect on bromine levels.
But it can take your fc from 5 to .5 overnight on a 24/7 injection system.
As for 4.6 turnovers... a 24/7 circulation system on a fractional hp pump (such as in your hot springs) is moving water at around 10gpm through the injection system. So if your spa is 400 gallons, that is a 40 minute turnover. 4.6 of those is 184 minutes, or about 3 hours for 99% ozone exposure. So 8 times per day your water is completely exposed to ozone.
Is there some theoretical risk? Sure. Do you still need chlorine? Yes.
Have I had any problems in the last 15 years or so I have done this? No.
Also, your jets running with the air injection on will aerate your water and raise your ph much more than the tiny bit in the ozone injection system. Close your air controls when not in use.
Just my 2 cents worth...
 

Spa user

New member
Mar 24, 2021
2
Temple City, Calif
Thank you for your responses. Just to get more specific here is a bit more information. Our spa is about 5 months old and is a Hot Springs Sovereign so I think 320 gallons. My wife and I are the only ones who use it and we use it pretty much nightly. The ozonator runs 24/7. I started to use either the MPS or dichlor after each usage and just hit the 10 minute clean cycle, close the lid then go in the house. But then I heard somewhere that you shouldn't close the lid right after putting in chemicals so now I add them the next morning where I can keep the lid off for awhile. I hate to sound dense here but I'm still not sure what to do chemical wise. Should I forget about the MPS and just use the dichlor? Should I put maybe a tablespoon in every day or just every few days to shock it? By the way I did notice a rise in my ph/ta so should I start adding spa down until it gets within the proper range? Also at this time I don't use any bromine. Only MPS and dichlor. Thanks for your patience. Oh. One more thing. I also have one of those silver ion cartridges in that one main filter housing.
 

mknauss

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May 3, 2014
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Sjde

Well-known member
Apr 29, 2016
297
Denver CO
When we got our ozonator , we started adding just enough MPS (non chlorine shock) or Dichlor to keep the bromine reading at 1-2 ppm. Before that it was 3-5ppm I think, but with an ozonator, we were told it could be lower.
 
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