Ozone and Sanitation

Joe kipp

Bronze Supporter
Aug 7, 2016
23
Lousiville, KY
So the new hot tub we have has an ozone generator on it to help with oxidation and presumably sanitation.

My understanding is that I should shock the pool after being in the pool and the ozone will remove the CC's and any FC left over after a period of time. So after each use we need to add cholerine, which we've got sodium dichloro-s-triazinetrione. I think that was in a post by @RDspaguy? I cannot find it now.

Thanks
joe
 
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Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
8,783
NY
Hey Joe !!

I wish I had realized how nasty we are when I had my hot tub. It was a constant battle because I couldn’t grasp something so simple at the time. I was clean, fresh from the shower with a fresh from the wash suit on. What’s the problem ????? !!! ????!

Then I hopped in 104 degree water and sweated my body oils off. And got free exfoliation of any dead skin. Plus residual soap, shampoo, conditioner, laundry detergent and fabric softener. (Although you can skip the last 2 sans pantiloons).

Then factor in keeping algae at bay, bacteria, viruses, pathogens etc. and yeah. We are NASTY.

Expect to use a few PPM of FC, per person, per 30 minutes. Whatever you started with will be gone by the time you get out and the people soup left behind will need enough new FC to get it all. The ozone will certainly help with sanitizing and also clearing the CCs from the chlorine doing it’s thing. But the key is to walk away leaving enough FC to clear the residuals.

Start a little high at the next soak and test/retreat immediately after. If you are getting a lot of use you will get a feel if you can skip the in between (daily) testing, by testing regularally until you know how your tub responds. If it’s a busy week and the tub has sat, expect to need regular doses to ensure it’s good when you have the time to soak again.

The dichlor is fine to use until it elevates your CYA. Then switch to plain bleach until your next refill. It lasts a long time so no need to use it up quickly.
 

A.O.

Well-known member
Apr 12, 2016
310
Kershaw, South Carolina
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
We have a 450 gal spa, use it twice a day, morning and evening. I have my water balanced, and pretty much add 1 3/4-2 oz liquid chlorine (10%) after every use (twice a day) and do not mess with it much more than that, other than the occasional MA to keep the PH in check. I never "shock" I just maintain the FC level.
 

RDspaguy

In The Industry
Mar 21, 2020
1,290
Cabool, Mo
You will want to watch your cya when using dichlor. Switch to bleach at 30ppm. Since dichlor is nearly half cya, once you have added 30ppm of chlorine you will have reached the recommended level of cya.
 

A.O.

Well-known member
Apr 12, 2016
310
Kershaw, South Carolina
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
So why is it that no one makes a powdered or tableted chlorine , why do they have to add the CYA? Obviously chlorine can be dried out, why not do it on its own?
 

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Joe kipp

Bronze Supporter
Aug 7, 2016
23
Lousiville, KY
Hey @A.O. We have a leslies right across the street from us but they seem overly expensive for most things and not very well stocked. I've been driving to Watsons about 5 miles away to pickup stuff for the hot tub. How's the Leslies near you stocked?
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
11,125
Franklin, NC
So why is it that no one makes a powdered or tableted chlorine , why do they have to add the CYA? Obviously chlorine can be dried out, why not do it on its own?
It's chemistry.

In it's natural state, chlorine is a gas. Many large commercial pools actually use gas injection systems to chlorinate their pools.

Now, to change chlorine into something we can use at home it needs to be bound to something to turn it into a solid. The "somethings" that are commonly used are:

Stabilizer (also known as CYA),

Calcium,

Lithium,

Or --- get this water.

All of these add a little salt to your water, but they add something else. Cal-Hypo add calcium, Tri-Chlor and Di-Chlor (tabs and most granules) add stabilizer, Lithium hypochlorite adds lithium and liquid chlorine adds - water.
 
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5tan

Active member
Jan 9, 2021
37
Canada
Pool Size
1643
Chlorine
Liquid Chlorine
Consider the effects of ozone to be secondary to chlorine. Ozone is an excellent backup to chlorine, but you absolutely still need a chlorine source for residual sanitizing power. Ozone does not provide any sort of residual - think of it like a super-instant-clean with zero lasting power, that only cleans the bits of water that touches the ozone gas. Not all of the water will touch the gas unless you run the ozonator long enough, but you also don't need it to either, so long as you have a free chlorine residual.

If you can, time your ozone to run immediately after your soaks for 0.5-4 hours (test the timing to see how quickly the ozone burns through your chlorine - see below about that). The post-soak ozonation will clean up waste quickly, and then add enough liquid pool chlorine to get to 6-10ppm FC in order to maintain a sanitizing residual in the water, keeping your water clean until your next soak. Ozonators usually run with filtration cycles and heating cycles, and only if the spa control panels have not been touched, as some manufacturers don't want to output ozone while spa is actively in use - check your owner's manual or techbook to confirm.

If your ozonator will continue to run after you add the liquid pool chlorine, shoot for 10ppm FC. The reason is because ozone destroys the hypochlorite ion to produce 77% chloride and 23% chlorate per the following reaction:

Chloride reaction: O3 + OCl- --> [ O2 + Cl-O-O- ] --> 2O2 + Cl- (77%)
Chlorate reaction: 2O3 + OCl- --> 2O2 + ClO3- (23%)

Basically, you will see much higher (~50% or more) chlorine demand (aka consumption, burn, utilization, destruction) whenever your ozonator runs. You want enough free chlorine to be circulating and sanitizing before the ozone destroys the chlorine, so you need to find a balance between ozonation and not destroying your free chlorine too quickly before it gets a chance to thoroughly sanitize the spa. If your ozonator is powerful and effective (e.g. Bullfrog EOS system), at 4 hours of daily ozonation (4hr filtration cycle), it can take your free chlorine below 1ppm within 3 days. This isn't necessarily a bad thing - if your spa is well sealed, the plumbing is biofilm-free, and the water and all surfaces are already sanitized from the previous free chlorine killing everything in sight, and no bacteria is growing on the underside of your cover, then having a sustained low FC level shouldn't be a concern since there is no bacteria in the closed-system to cultivate.

However, prior to your next soak, you should raise FC to 3-6ppm, since going in for a soak will shed billions of bacteria off your skin and into the water instantly, some of which can multiply very quickly (some populations double every 20 minutes) when there is <3ppm FC.

Free Available Chlorine Germ-Killing Timetable
E. coli 0157:H7 (Bacterium): less than 1 minute
Hepatitis A (Virus): approximately 16 minutes
Giardia (Parasite): approximately 45 minutes
Cryptosporidium (Parasite): approximately 15,300 minutes (10.6 days)
Note: Times based on 1 ppm free chlorine at pH 7.5 and 77°F (25°C). These disinfection times are only for pools and hot tubs/spas that do not use cyanuric acid. Disinfection times are longer in the presence of cyanuric acid.
Source: Disinfection & Testing | Healthy Swimming | Healthy Water | CDC

I find the following article about ozone to be excellent and unbiased: Unfiltered Truth About Ozone in Hot Tubs - many (most) other websites have some incorrect information mixed in or are heavily biased towards selling ozone generators without noting the many caveats required to substantiate their claims about the benefits of ozone.
 
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A.O.

Well-known member
Apr 12, 2016
310
Kershaw, South Carolina
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Hey @A.O. We have a leslies right across the street from us but they seem overly expensive for most things and not very well stocked. I've been driving to Watsons about 5 miles away to pickup stuff for the hot tub. How's the Leslies near you stocked?
Pretty good most of the time. But its about an hour away, we live way out in the middle of nowhere.. nothing very close. last time I got a case of 4 gallons for 20 bucks.
 
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