CYA in a bromine spa

Sjde

Well-known member
Apr 29, 2016
112
Denver CO
I was never paying attention to CYA because I didn’t think I had to but now that I use a little bit of dichlor does that change everything?

Also, according to what I’ve read , apparently even in a bromine spa using MPS only and bromine tabs , there is still some chlorine in there from the chemical reaction or from the tabs? Thanks!
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,847
Tucson, AZ
Which bromine tabs are you using? There a several different formulations of solid brominating tablets on the market. Many tablets use BCDMH (1-Bromo-3-chloro-5,5-dimethylhydantoin). BCDMH adds both chlorine and bromine to the water. If excess bromide ion is in the water (say, from adding sodium bromide) or there is spent bromine in the spa (sanitizing bromine is reduced to bromide), then the chlorine from the BCDMH will simply activate (oxidize) the bromide back into sanitizing bromine (the chlorine is then converted into chloride ion).

If Dibromodimethylhydantoin (DBDMH) is used, then only sanitizing bromine is formed in the water and you would need to add a chlorine product (bleach or dichlor) to activate any spent bromide. Ozone can also oxidize bromide back into bromine. MPS is slower at oxidizing bromide into bromine but it can be used. However, if one uses MPS, it can interfere with the standard DPD halogen test chemicals and confuse the results. Thus, you typically want to avoid regularly using MPS for activation purposes.
 

Sjde

Well-known member
Apr 29, 2016
112
Denver CO
Which bromine tabs are you using? There a several different formulations of solid brominating tablets on the market. Many tablets use BCDMH (1-Bromo-3-chloro-5,5-dimethylhydantoin). BCDMH adds both chlorine and bromine to the water. If excess bromide ion is in the water (say, from adding sodium bromide) or there is spent bromine in the spa (sanitizing bromine is reduced to bromide), then the chlorine from the BCDMH will simply activate (oxidize) the bromide back into sanitizing bromine (the chlorine is then converted into chloride ion).

If Dibromodimethylhydantoin (DBDMH) is used, then only sanitizing bromine is formed in the water and you would need to add a chlorine product (bleach or dichlor) to activate any spent bromide. Ozone can also oxidize bromide back into bromine. MPS is slower at oxidizing bromide into bromine but it can be used. However, if one uses MPS, it can interfere with the standard DPD halogen test chemicals and confuse the results. Thus, you typically want to avoid regularly using MPS for activation purposes.
We have the first.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,847
Tucson, AZ
If they are BCDMH tablets, then no additional oxidizer is needed (no MPS). You simply fill the floater and adjust the opening to achieve a stable Br level. Just note that bromine floaters are not very accurate/reliable devices. At first you might get the right opening setting and then find a few days later that it’s not keeping up. You could wind up chasing your tail a lot with it. An ozonator on the spa helps to keep a more consistent Br level but they are notorious on hot tubs for being unreliable as they are usually low-end, cheap units with poor output.

Just keep an eye on your pH and TA because you don’t want those to crash on you. If the water turns yellow/brown color, that’s an indication of very acidic water conditions in brominated water.
 

Sjde

Well-known member
Apr 29, 2016
112
Denver CO
If they are BCDMH tablets, then no additional oxidizer is needed (no MPS). You simply fill the floater and adjust the opening to achieve a stable Br level. Just note that bromine floaters are not very accurate/reliable devices. At first you might get the right opening setting and then find a few days later that it’s not keeping up. You could wind up chasing your tail a lot with it. An ozonator on the spa helps to keep a more consistent Br level but they are notorious on hot tubs for being unreliable as they are usually low-end, cheap units with poor output.

Just keep an eye on your pH and TA because you don’t want those to crash on you. If the water turns yellow/brown color, that’s an indication of very acidic water conditions in brominated water.
Well that’s good to know.

So I don’t need to measure CYA?
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,847
Tucson, AZ
The CYA is not going to affect bromine. Theoretically, high CYA levels could slow down the conversion of bromide into bromine because the CYA would make the hypochlorous acid (HOCl) levels a lot lower, but that would be really hard to see....and you'd need very high levels of CYA. SO if you're using dichlor to activate bromide back into bromine, that's fine. Just know that with a bromine tub, you'll probably want to be very strict on dumping the tub every 3 months or so to make sure the water is fresh. As long as you keep the tub plumbing properly purged (use Ahh-some) and the chemistry in line, using bromine shouldn't be too hard.

As a side note, I would not use the MPS very regularly. MPS can activate bromine BUT it also adds a lot of sulfates to the water and sulfates will attack the metal in your tub heater faster than chlorides will. So regular and frequent use of MPS can have significant downsides for your hot tub's heater.
 

Sjde

Well-known member
Apr 29, 2016
112
Denver CO
The CYA is not going to affect bromine. Theoretically, high CYA levels could slow down the conversion of bromide into bromine because the CYA would make the hypochlorous acid (HOCl) levels a lot lower, but that would be really hard to see....and you'd need very high levels of CYA. SO if you're using dichlor to activate bromide back into bromine, that's fine. Just know that with a bromine tub, you'll probably want to be very strict on dumping the tub every 3 months or so to make sure the water is fresh. As long as you keep the tub plumbing properly purged (use Ahh-some) and the chemistry in line, using bromine shouldn't be too hard.

As a side note, I would not use the MPS very regularly. MPS can activate bromine BUT it also adds a lot of sulfates to the water and sulfates will attack the metal in your tub heater faster than chlorides will. So regular and frequent use of MPS can have significant downsides for your hot tub's heater.

Thank you.

My original concern was if I needed to measure CYA ( like you do in a pool or a chlorine hot tub) and dump the water when it gets too high. I hadn’t been paying attention to that reading.

When I started with this spa and decided to do bromine rather than chlorine, I thought that meant no dichlor should be used at all, just MPS.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,847
Tucson, AZ
Thank you.

My original concern was if I needed to measure CYA ( like you do in a pool or a chlorine hot tub) and dump the water when it gets too high. I hadn’t been paying attention to that reading.

When I started with this spa and decided to do bromine rather than chlorine, I thought that meant no dichlor should be used at all, just MPS.
Chlorine is used as the oxidizer to convert bromide ion (Br-) to sanitizing hypobromous acid (HOBr). When the chlorine oxidizes the bromide it gets reduced to chloride ion (Cl-), basically salt. So the use of chlorine is not significant. As long as the bromide ion concentration is larger than the amount of chlorine added, there will be no chlorine in the water after a very short period of time. This happens because the conversion of bromide to bromine is an extremely fast chemical reaction and it goes totally to completion. This is why a bromide “bank” of 30ppm is suggested - that is a lot more bromide ion as compared to a few ppm of chlorine.

The only way to not use chlorine is to use a different oxidizer. Ozone is typically added to a hot tub by a corona discharge ozone generator. However, those devices are typically very inefficient and don’t last long. There’s also no indication when they fail so a tub owner will not know right away that the unit is not working.

Potassium monopersulfate (MPS) is another oxidant but it is slow to convert bromide to bromine. It is quite acidic and leaves sulfates behind as a by product. Sulfates are typically more damaging to metal tub components than chlorides especially if the pH gets too low.

The best way to convert bromide to bromine is to use regular, unscented laundry bleach as it is sodium hypochlorite and the only excess it adds is a little bit of salt. Liquid chlorine itself has a slightly basic effect on water and mildly raises pH. That is easily overcome with a little bit of muriatic acid.
 

Sjde

Well-known member
Apr 29, 2016
112
Denver CO
Yes, we were told we had to use either chlorine ( dichlor) or MPS as a sanitizer in our bromine tub.

We started out with MPS because I wanted to stay away from chlorine for some reason, but then we were having trouble clearing up the cloudiness, so started also adding a bit of chlorine.
 

Sjde

Well-known member
Apr 29, 2016
112
Denver CO
Chlorine is used as the oxidizer to convert bromide ion (Br-) to sanitizing hypobromous acid (HOBr). When the chlorine oxidizes the bromide it gets reduced to chloride ion (Cl-), basically salt. So the use of chlorine is not significant. As long as the bromide ion concentration is larger than the amount of chlorine added, there will be no chlorine in the water after a very short period of time. This happens because the conversion of bromide to bromine is an extremely fast chemical reaction and it goes totally to completion. This is why a bromide “bank” of 30ppm is suggested - that is a lot more bromide ion as compared to a few ppm of chlorine.

The only way to not use chlorine is to use a different oxidizer. Ozone is typically added to a hot tub by a corona discharge ozone generator. However, those devices are typically very inefficient and don’t last long. There’s also no indication when they fail so a tub owner will not know right away that the unit is not working.

Potassium monopersulfate (MPS) is another oxidant but it is slow to convert bromide to bromine. It is quite acidic and leaves sulfates behind as a by product. Sulfates are typically more damaging to metal tub components than chlorides especially if the pH gets too low.

The best way to convert bromide to bromine is to use regular, unscented laundry bleach as it is sodium hypochlorite and the only excess it adds is a little bit of salt. Liquid chlorine itself has a slightly basic effect on water and mildly raises pH. That is easily overcome with a little bit of muriatic acid.

Our spa does have a built-in ozonator but I’ve heard they only last 2 to 3 years and there’s no way to know when they are not working because ours only comes on when the jets are on . In other models of tubs , I think they come on when the jets are not on , so you would see the bubbles if it’s working.
 

Sjde

Well-known member
Apr 29, 2016
112
Denver CO
Someone on one of these threads posted-

Just know that with a bromine tub, you'll probably want to be very strict on dumping the tub every 3 months or so to make sure the water is fresh.”

That’s more important in a bromine spa?
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,847
Tucson, AZ
Yes, we were told we had to use either chlorine ( dichlor) or MPS as a sanitizer in our bromine tub.

We started out with MPS because I wanted to stay away from chlorine for some reason, but then we were having trouble clearing up the cloudiness, so started also adding a bit of chlorine.

MPS is not recognized by the EPA as a sanitizer for recreational water (hot tubs and pools). The only way the EPA recognizes MPS as a sanitizer is if it is used in conjunction with silver ions and, even then, the water temperature must be above 98F in order for there to be a short enough pathogen kill time.

Our spa does have a built-in ozonator but I’ve heard they only last 2 to 3 years and there’s no way to know when they are not working because ours only comes on when the jets are on . In other models of tubs , I think they come on when the jets are not on , so you would see the bubbles if it’s working.
Yes, this is the problem in most tubs that are sold with ozonators. They are unreliable.


Someone on one of these threads posted-

Just know that with a bromine tub, you'll probably want to be very strict on dumping the tub every 3 months or so to make sure the water is fresh.”

That’s more important in a bromine spa?

Regular water exchanges are important in all hot tubs no matter the sanitation method. Hot tubs are very low water volume and thus the bather load is very high. Sweat, urine and organics will build up in the water quickly and they can not all be oxidized away. Chlorinated organics can persist for very long times and this is usually seen as a constant CC level that builds up slowly and can not be gotten rid of with shock chlorination. Brominated organic compounds are worse in terms of human health - when looking at similar organic compounds that contain either chlorine or bromine, brominated organics are often more carcinogenic than chlorinated analogues. As well, bromide ions actually generate two different oxidized species when they react with an oxidizer - sanitizing bromine AND/OR bromates (BrO3-). Bromates are formed at a lower rate than bromine but they are still formed. Bromates are known carcinogens and, while skin absorption is not an issue, bromine can not be used in drinking water sanitizing applications for this very reason - the formation of bromates is considered a danger to potable water supplies.

My honest personal opinion is that bromine is no safer to use than chlorine (in fact, it is less safe in my opinion) and it is far more expensive to use. You have to use another oxidizer to activate the bromine so, at the end of the day, you are using more chemicals and more expensive chemicals to run a tub with bromine. Bromine is not anymore stable in a hot tub than chlorine and the argument that it has a higher pKa and therefore you get more sanitizer concentration out of it is specious at best. Chlorine is safe, effective and easy to use...and cheap. It really is a shame that the hot tub industry plays these silly games with chemicals and tries to make chlorine out to be the bad-guy.
 

Sjde

Well-known member
Apr 29, 2016
112
Denver CO
“MPS is not recognized by the EPA as a sanitizer for recreational water (hot tubs and pools). The only way the EPA recognizes MPS as a sanitizer is if it is used in conjunction with silver ions .”

I did not know this . Our hot tub manufacturer and retailer indicated we could use MPS . This tub did come with something called a Spa Frog that had a silver ion cartridge but we chose not to use it because the cartridge had to be replaced frequently and was not inexpensive. I didn’t think it was required . It is supposed to enable you to use fewer chemicals.
 

Sjde

Well-known member
Apr 29, 2016
112
Denver CO
Yes , most everything you read says bromine is superior for hot tubs . I thought it was more stable , and easier on your skin.

So if we wanted to switch from a bromine spa to a chlorine one, what is the procedure? And what products do you need?

One factor I hadn’t mentioned though, is that this is in a vacation rental and that might make a difference.
 

Sjde

Well-known member
Apr 29, 2016
112
Denver CO
I am not sure but I think in a chlorine spa, it is critical to add chlorine every day or after use ? And renters are not going to be good about doing that . We can’t afford to pay someone to come in every day to do it and we are 75 miles away.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,847
Tucson, AZ
“MPS is not recognized by the EPA as a sanitizer for recreational water (hot tubs and pools). The only way the EPA recognizes MPS as a sanitizer is if it is used in conjunction with silver ions .”

I did not know this . Our hot tub manufacturer and retailer indicated we could use MPS . This tub did come with something called a Spa Frog that had a silver ion cartridge but we chose not to use it because the cartridge had to be replaced frequently and was not inexpensive. I didn’t think it was required . It is supposed to enable you to use fewer chemicals.
Precisely. The "Frog" system cartridges adds the silver ions (silver nitrate embedded in a slowly dissolving matrix) and the MPS acts mainly as the oxidizer for bather waste. Silver ions are known to be anti-viral and anti-bacterial when in solution and at higher temperatures (104F). The MPS enhances the ability of the silver ions to kill pathogens and somewhat stabilizes the silver ion in solution (silver will readily form insoluble oxides and chlorides when in aqueous solution). The down side to these systems is that there is no way to know what the silver concentration is nor is it easy to figure out how much MPS is in the water, so reliable testing and accurate dosing are out the door and you have to rely on trial and error. Not the best way to manage a body of water.

Yes , most everything you read says bromine is superior for hot tubs . I thought it was more stable , and easier on your skin.

So if we wanted to switch from a bromine spa to a chlorine one, what is the procedure? And what products do you need?

One factor I hadn’t mentioned though, is that this is in a vacation rental and that might make a difference.
I am not sure but I think in a chlorine spa, it is critical to add chlorine every day or after use ? And renters are not going to be good about doing that . We can’t afford to pay someone to come in every day to do it and we are 75 miles away.
The devil is in the details with bromine. The upside of bromine is that, because of it's chemistry in water, sanitizing bromine is almost 99% in the form of hypobromous acid (HOBr) as opposed to hypobromite ion (OBr-). Chlorine, on the other hand, is about 50/50 hypochlorous acid/hypochlorite at a pH of 7.5. So one can make the argument that you have more active sanitizer available with bromine. However, why should that matter? As long as the sanitizing compound is at concentration high enough to kill pathogens at a reasonable rate, it doesn't much matter which one creates more as any excess sanitizer is going to oxidize organics, bathing suits, skin, etc. In fact, some of the oxidation reactions with organic compounds, especially nitrogen containing compounds, are sensitive to the concentration of the oxidizer and, if high enough, you can create more of the nastier smelling stuff. The beauty of chlorine and cyanuric acid is that the CYA acts as a very good buffer for the chlorine concentration and so it greatly reduces the harshness of chlorine in water. The similar analogue of CYA for bromine is DMH but it takes A LOT more DMH to have the same buffering effect on bromine as it does compared to CYA & Chlorine.

As well, both bromine and it's combined nitrogen compound, monobromamine, are effective sanitizers while the corresponding combined chlorine compound, monochloramine, is not an effective sanitizer. However, no one really wants combined bromine compounds around because they tend to smell harsh and irritate mucous membranes. One advantage of chlorine is that you can measure free chlorine separately from combined chlorine and so you can have an easy indicator (the CC concentration) for when it's time to dump the tub. For bromine, the test kit only measured Total Bromine (TB = sanitizing bromine + combined bromines) and so you have no idea if the water contains 100% sanitizing bromine, 100% combined bromine or some fractional split. Thus, aside form a bad smell, you have no good way to know when you should dump the tub.

As for being "easier on the skin" that's totally subjective. There are some people that can't smell bromine compounds nor are sensitive to them and there are others who gag at the smell of bromine and get skin rashes from brominated water. It all depends on the person.

If you can't be there daily or even every few days to manage a tub, then any sanitizer is going to have it's drawbacks. There are salt-water chlorine generators for hot tubs that you can hang over the side of the tub when not in use and it will generate small amounts of chlorine automatically. Some people on the forum here use them and like them a lot. The only downside is that you do have to add salt to your tub water and, if the manufacturer doesn't allow for that, you will void your warranty (if you have any warranty left). Again, I personally think it's a load of baloney to void a warranty for that but the manufacturers don't really listen to reason. Usually when converting a tub to use salt water, one has to have the heater replaced with a higher-end model (typically a titanium heater as opposed to Incoloy or teflon coated steel) to avoid chloride corrosion.

You can stick with bromine in a floater as this is a rental, but I don't think any system is all that reliable in a remote application and, for sure, renters are not going to bother themselves with proper hot tub use and care. There would seem to me to be much more liability on you, the landlord, having a hot tub at a rental that could be potentially dangerous to people (from a health/disease perspective), then to simply shut it down when you are not there and lock the top of it. Then again, a rental with a pool can be equally or more dangerous and so I hope you have good general liability insurance for such matters ;)
 

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