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Ozonator Affecting Chlorine Readings


RonB01
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Another newbie here. I just bought a Hot Springs Vanguard. The saleswoman says that the ozonator will cause the chlorine test to read lower than actuality. Is this fact or fluff?

Thanks to this forum for the information leading to my purchase, and hopefully taking some of the pain out of the initial learning curve :-)

Regards,

RonB

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Half correct. Chlorine and ozone tend to destroy each other. Ozone reduces chlorine sanitizer into chloride ions in the water and in the process is converted into oxygen. Ozone CAN lower the chlorine levels in the water and they will then test lower than you expect then to. That means you need to add additional chlorine to compensate for that.

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Thanks, Waterbear. Off to the store this afternoon to (hopefully) get a decent test kit.

Your best bet is a Taylor K-2006. Don't get the K-2005. The K-2006 has a MUCH better and easier to read chlorine test and it has a much wider range. Otherwise the kits are identical and will test all the parameters you need in a chlorine spa.

If you cannot find the K-2006 locally (which is usually the case) it can be ordered directly from Taylor Technologies and from various online retailers.

Amato Industries has one of the lowest prices but I have heard that their shipping times are slow.

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Well, the dealer sent a handful of chemicals but no test anything, not even test strips. How do they expect someone to be happy with a hot tub without being able to properly take care of the water? Maybe they figure ignorance is bliss, and bad water maintenance will allow them to deny warranty claims :-(

The local pool store had a couple types of test strips and one really lame looking drop kit: it only tested two things! So, let's try something else...

Anyway, I let my fingers do the walking to try and get a test kit quickly.

Taylor Industries wanted to charge an extra $25 for an "expedited order", which meant it would ship the next day and take 2 days from their location (MD) to mine (NC). Overnight shipping is not available due to the test kits being "hazardous materials"; I should have realized that and planned ahead, but didn't.

The list of suppliers on Taylor's web site was not helpful, either. They either were commercial-only suppliers and didn't even want to talk to me, or didn't stock the test kit.

Google Shopping listed several online pool supply companies that claimed to have them in stock, but they were all 2 or more shipping days away from me. I finally found one in Springfield, VA that had it, so I gave them a call to see what they could do. By now it is 4:30 in the afternoon. The helpful young man who took my order first checked with shipping to see if they could get it out that day. He came back and said that they could if the order was taken quickly. He took my information, ran the credit card, and verified that it went through and they would get it out that day.

This morning, we have a "snow event", so I didn't know if it would get here or not. But, about quarter past ten, UPS showed up and dropped the package off! Color me impressed with their level of service.

I got my test kit from pool center dot com.

Edited by RonB01
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Well, the dealer sent a handful of chemicals but no test anything, not even test strips. How do they expect someone to be happy with a hot tub without being able to properly take care of the water? Maybe they figure ignorance is bliss, and bad water maintenance will allow them to deny warranty claims :-(

The local pool store had a couple types of test strips and one really lame looking drop kit: it only tested two things! So, let's try something else...

Anyway, I let my fingers do the walking to try and get a test kit quickly.

Taylor Industries wanted to charge an extra $25 for an "expedited order", which meant it would ship the next day and take 2 days from their location (MD) to mine (NC). Overnight shipping is not available due to the test kits being "hazardous materials"; I should have realized that and planned ahead, but didn't.

The list of suppliers on Taylor's web site was not helpful, either. They either were commercial-only suppliers and didn't even want to talk to me, or didn't stock the test kit.

Google Shopping listed several online pool supply companies that claimed to have them in stock, but they were all 2 or more shipping days away from me. I finally found one in Springfield, VA that had it, so I gave them a call to see what they could do. By now it is 4:30 in the afternoon. The helpful young man who took my order first checked with shipping to see if they could get it out that day. He came back and said that they could if the order was taken quickly. He took my information, ran the credit card, and verified that it went through and they would get it out that day.

This morning, we have a "snow event", so I didn't know if it would get here or not. But, about quarter past ten, UPS showed up and dropped the package off! Color me impressed with their level of service.

Moderator: Can I actually post the name or link of the company? or, do I have to wait until I have more posts before doing so?

I believe you can post the link. If not just put spaces between the www (w w w ) part and it should post. By all means post the name. IMHO, it would be good to know a company that provides this level of service. How much did they charge you for the kit?

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Hey Ron, the main reason people buy ozone is to reduce the amount of chlorine you need. So, keep it between .5 and 1 PPM. The more ozone you have, the less chemicals you need (so, circulation time and ozone output are factors).

In the field, I see a LOT of tubs that are chemically abuses, and many think they still need 3 PPM of chlorine or bromine, but that' not true. Overuse of chemicals wears out your equipment and cover faster.

Yes, ozone and chlorine will eat each other. Get this picture: ozone is SO FAST, it's not typically in the spa where the chlorine is. Ozone wants to go after soft-celled particles first, such as viruses and bacteria. If ozone has nothing better to attack, and chlorine is in its path, they will break each other down.

Take it easy and enjoy your tub!

Jennifer at DEL Ozone

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Whether ozone reduces or increases chlorine demand in a spa depends on the bather load. For spas that are used every day or two, an ozonator usually cuts the chlorine demand roughly in half. However, for infrequently used spas, say once a week or so, an ozonator typically doubles the chlorine demand from roughly 25% loss per day to 50% loss per day. This is because ozone can oxidize chlorine to chlorate and the injected air may also accelerate its outgassing. So when there is reasonable bather load, then ozone can oxidize bather waste faster than chlorine, thus lowering chlorine demand, but when there isn't, it uses up chlorine instead. This is consistent over and over again on spas with ozonators reported on this and other forums.

As for the level of chlorine needed, that is an entirely different matter. What I described above was the total amount of chlorine that is used and needs to be replenished. That is not the same thing as the actual Free Chlorine (FC) level that is needed. It is not true that you can have as low a chlorine level as you describe because it is very hard to prevent it going to zero in that situation and would become low enough towards zero to allow bacteria to grow, especially in biofilms on surfaces that won't get circulated through the ozonator. An ozonator is a supplemental oxidizer, not a bulk sanitizer. So the chlorine level in the bulk spa water still needs to be substantial enough to not run out.

4 ppm FC with 30 ppm CYA is equivalent in hypochlorous acid concentration to around 0.6 ppm with no CYA in a hot (104ºF) spa so is low enough to minimize oxidation of skin, swimsuits and hair as well as outgas. Cyanuric Acid (CYA) is an active chlorine (hypochlorous acid) buffer (see this paper). In practice, for those who want to minimize the amount of chlorine during their soak and have virtually no smell, they can start with around 1-2 ppm FC at the start of their soak and add more chlorine after their soak such that they get to 1-2 ppm again at the start of their next soak. That ensures enough extra that they won't get to zero between soaks though they will get to zero sometime during their soak (that's a risk most people are willing to take as bacterial growth is 15-60 minute doubling time and person-to-person transmission of disease risk is usually low in a residential spa). For those who want a no chlorine during the soak approach, Nature2 (silver ions) with MPS can be used along with weekly shocking with Dichlor (or Dichlor-then-bleach).

The bottom line is that if one uses a spa a lot, then an ozonator can be helpful, but if they do not, then it can end up using more chemicals than not having the ozonator.

Richard

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Ozone primarily reduces chlorine to chloride. There are two different reactions of ozone with hypochlorite ions.

O3 + OCl- --> 2O2 + Cl-

ozone + hypochlorite --> oxygen + chloride ion

2 O3 + OCl- --> 2O2 + ClO3-

ozone + hypochlorite --> oxygen + chlorate

The first reaction accounts for 77 % of the reactions and the second reaction accounts for 23 % of the reactions.

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Well, I think I may be getting it dialed in.

CH 120

TA 60

pH 7.6

FC 5.0

CYA 42

Borates 16

CSI -0.27

I am adding ~6 oz Chlorox each night so that my FC is above zero when I get home from work, so it can continue to drop until I soak at night, then add some more after to keep it well above zero until the next day. This is with ~2 bather/hours per day on average.

Every few days, I need to bring the pH down a few points. Maybe next time I fill I will try for CH 100, FC 80 and see if that is more stable.

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Every few days, I need to bring the pH down a few points. Maybe next time I fill I will try for CH 100, FC 80 and see if that is more stable.

I think that you mean CH 100 and TA 80?

You don't want a higher TA; a higher TA will cause more pH rise. To reduce pH rise, you can use a higher pH and a lower TA. Using a pH of 7.6 to 7.9 and a TA of 40 to 70 should give good stability.

Right now, you could increase your borates to 50 for more pH buffering. You could also target a slightly higher pH of 7.8 to reduce pH rise. If you increase your borates to 50 ppm, then you could target a pH of 7.9.

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Every few days, I need to bring the pH down a few points. Maybe next time I fill I will try for CH 100, FC 80 and see if that is more stable.

I think that you mean CH 100 and TA 80?

That is exactly what I meant.

So, next fill I will target CH 100, TA 50, and see how that works.

Plugging those numbers into thepoolcalculator, I get a CSI of -0.37. Is that close enough to zero to not worry about?

Thanks for all the help.

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I would try to keep the CSI between -0.3 and -0.1. Your numbers are pretty good right now. I think that if you started to use a pH of 7.8 or 7.9, your pH would be more stable.

The right TA is going to depend on where you want to keep the pH. The lower you want to keep the pH, the lower you need to keep the TA to maintain a stable pH. A pH of 7.8 to 7.9 should be stable with a TA of 60 ppm. If you wanted to use a pH of 7.5 or 7.6, then you will probably need to use a TA of 50 ppm.

Once you get the pH and TA stable, then you want to adjust the Calcium to where you get in the -0.3 to -0.1 range.

The offgassing of carbon dioxide causes the pH to rise. The rate of offgassing depends on factors such as temperature, aeration and the concentration of carbon dioxide. This chart shows the concentration of carbon dioxide in ppm at various pHs and TAs (TA as carbonate alkalinity).

.......................................................TA 100...TA 80....TA 60....TA 50

pH..........X........%CO2....%HCO3.... CO2........CO2.......CO2......CO2

7.5......-1.15........6.61..........93.39......6.23.........4.98........3.74.......3.12

7.6......-1.25........5.32..........94.68......4.94.........3.95........2.96.......2.47

7.7......-1.35........4.28..........95.72......3.93.........3.14........2.36.......1.97

7.8......-1.45........3.43..........96.57......3.12.........2.50........1.87.......1.56

7.9......-1.55........2.74..........97.26......2.48.........1.98........1.49........1.24

There is the same amount of carbon dioxide dissolved in the water at the following:

pH = 7.5 and TA = 50

pH = 7.7 and TA = 80

pH = 7.8 and TA = 100

or

pH = 7.6 and TA = 50

pH = 7.8 and TA = 80

pH = 7.9 and TA = 100

Increasing the pH by only 0.3 will allow you to maintain a TA of about 50 ppm higher with about the same amount of stability. Every 0.1 increase in the pH corresponds to an increase in TA of about 17 ppm for the same stability.

I think that you will begin to see good stability at a carbon dioxide concentration of about 2 ppm or less, such as pH =7.7 and TA =50, or PH = 7.9 and TA =80. However, this is still above the Henry's law concentration of aqueous Carbon dioxide, which is 1.2 x 10^-5 mole per liter at 25 C (77 F), which equals 0.528 ppm.

Chem geek has a chart here that shows a similar thing.

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IMHO, it would be good to know a company that provides this level of service. How much did they charge you for the kit?

It was poolcenter . com.

I got the 2oz kit (K-2006C) instead of the 3/4oz kit (K-2006) figuring I won't run out during the first year. If I don't use that much chemical, I can just get 3/4oz refills when I need them. They charged $96 for the kit (about $30 more than the 3/4oz kit), and $6 for shipping to a business.

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I would try to keep the CSI between -0.3 and -0.1. Your numbers are pretty good right now. I think that if you started to use a pH of 7.8 or 7.9, your pH would be more stable.

Yes, my numbers are looking pretty stable now.

CH 125

TA 70

pH 7.6

FC 6

CSI -0.24

I am still working on zeroing in out exactly how much chlorine to use each day, and putting in the boric acid a bit at a time (I am leery of dumping a pound of anything in the tub at one time). I'll let the pH get up a bit more before trying to bring it down.

Thanks again.

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  • 3 weeks later...

Well, this is a pretty boring subject. My water is still sparkling clean, and doesn't have bad odors.

The numbers are staying quite stable. I use the tub every day when home. My wife and I went on vacation for a week, and told the daughter to put in 6oz Chlorox every day. Some days she used the tub, some days not. When I got back, the pH was at 7.0, and everything else was right where I left it. I ran the pumps for maybe an hour the first night back, and the next afternoon the pH was back at 7.6, where it has stayed ever since.

Typical numbers:

CH 125 (I get 110 if I use the 10ppm/drop procedure)

TA 75

pH 7.6

FC between 0-1 @ 6pm; add 6-8 oz. Chlorox at end of day

CYA 43

CSI -0.18

I did bump the temperature up from 100 to 102; it feels a bit better on cold days.

I will shortly be coming up on the first month of ownership. I do have a fair amount of sudsing due to (I'm guessing) detergent and skin cream (at least I think I do; this is my first tub). I have a new set of filters to change out when I change water, so I don't have to rush through cleaning them.

Thanks to this forum, water treatment does not look to be an issue.

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  • 11 months later...

Hello again

I just wanted to thank the group for the information on getting the water dialed in.

That aspect of pool ownership has been actually boring :)

I change filters once a month, swapping in a spare set. I built a rack for the dishwasher, holding them upright instead of laying on their side. Then I soak them overnight in tsp & hot water, run them through the dishwasher again,then hang them out to dry.

When I change the water (every 3 or 4 months), I "sneak up" on the balance, only adding enough of each chemical to bring the water halfway to where I want it to be, letting it settle overnight, then re-testing and adding more until it's close enough.

From that point, I just add chlorine daily, and test weekly to make sure the water hasn't gotten too far out of whack.

I have had problems with the spa, though: lights, leaks, and the control panel. The dealer has handled them, though. It does give me concern for long-term reliability once it's out of warranty, though.

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I'm glad things are working out for you and hope that your spa problems being handled by the dealer are just short-term and don't occur after the warranty expires.

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  • 2 years later...

Hi,

I'm having trouble with the ozonator chlorine balance.

I have the new del ozone spa eclipse (50-70 mg.hr ozone). I have filtration at 4 hrs per day.

I am adding 2 oz chlorine (8.25%) after use.

The problem? Hot tub rash!

Everything else is balanced (CA 300, TA 50, PH 7.6 CYA 30). Is it possible to eliminate chlorine completely and just use ozone? If the ozone is eating the coloring, what is the point of adding chlorine?

If the ozone is insufficient, then what is the point of ozone?

Thanks!

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2 fluid ounces of 8.25% bleach would handle only around 30-35 person-minutes of soaking in a hot tub. How long are you soaking? Also, what was the FC level when you started your soak? It sounds like it was zero or near zero, is that correct or did the chlorine get too low in between soaks? How often are you soaking? If you don't soak every day or two, then using chlorine in a spa with an ozonator is harder to do since ozone reacts with chlorine so increases chlorine demand in between soaks.

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2 fluid ounces of 8.25% bleach would handle only around 30-35 person-minutes of soaking in a hot tub. How long are you soaking? Also, what was the FC level when you started your soak? It sounds like it was zero or near zero, is that correct or did the chlorine get too low in between soaks? How often are you soaking? If you don't soak every day or two, then using chlorine in a spa with an ozonator is harder to do since ozone reacts with chlorine so increases chlorine demand in between soaks.

Thanks chem geek. I typically soak around 30 to 45 minutes. FC is always at zero the next day, even if I shock with 12 fl oz of 8.25 % bleach. I am thinking it is the ozone which eats it all up. I soak in the evening and then the ozone goes on at midnight and then midday for 6 hours total filtration.

I have started putting in 6 oz per day of 8.25% bleach. The FC still reads zero the next day, but the water seems clearer. I have also hypothesized that the guilty bacteria may be growing where the cover meets the rim or some such place. I will give the cover a good clean.

Are you recommending an alternative system? Even 6oz of bleach per day is only about $4 per month, which is not too bad.

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Did you ever decontaminate your spa? Maybe you've got biofilms. At your next water change, superchlorinate and then add Ahh-Some and circulate (including jets) and then change the water (you can dechlorinate using hydrogen peroxide before dumping the water). That should get you to a decent baseline.

It's also possible that you got way behind in oxidizing bather waste, but that seems unlikely with the ozonator. Also, if you did not use Dichlor initially, then the chlorine can outgas too quickly, but you measured 30 ppm CYA so I presume you started out using Dichlor to build up the CYA level.

If you suspect the ozone as being the primary source of chlorine demand, then you can turn it off (disconnect it's air input or it's electrical input temporarily). When using the spa every day, usually the ozone reduces chlorine demand because ozone will oxidize some of your bather waste so that chlorine doesn't have to. If it's not the ozone, then I suspect biofilms. You should check/clean your filter as well.

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I was planning a decontamination at the next change, but that won't be for a couple of months. I think I was just being cheap with the chlorine. I now add 6-8 oz 8.25% bleach after soaking. The water is definitely clearer. I will try this for a while and see how it goes. I'm also going to reduce filtration to 4 hours total instead of 6 as the tub is overheating (according to Nordic, this is fine). I am hoping this will be enough ozone. At 50mg/hr, this is 200mg total, so we'll see.

I did use dichlor at the beginning, but I understand this is unnecessary unless there is sun exposure. I wasn't planning on using dichlor anymore. I will keep testing and let you know.

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No, it is not true that the Dichlor "is unnecessary unless there is sun exposure". You need the CYA in the water to moderate chlorine's strength. If you just added bleach without adding Dichlor first to build up some CYA, then the chlorine would be too strong and would oxidize your swimsuit, skin and hair too quickly, would outgas faster, would oxidize the hot tub cover faster, etc. CYA is not just there to protect chlorine from breakdown from the UV from sunlight. It is an active chlorine buffer that moderates its strength.

Have you read the Dichlor/bleach Method In A Nutshell sticky? You must use Dichlor initially after a fresh refill and should also use it about once a month since CYA drops by around 5 ppm per month by being slowly oxidized by chlorine. Also, though the sticky refers to 80 ppm TA, I would lower it to closer to 50 ppm TA to reduce the rate of pH rise and also use 50 ppm Borates (usually from boric acid) as an additional pH buffer.

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