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Salt Water Vs Bcdmh With Or Without Ozone Or Uv-C Light


Terv

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I asked Del Ozone why ozone is not recommended to be used with bromine except in residential spas. Why is it safe for residential spas? No reply as yet.

Most information I am finding on UV-C light is in combination with chlorine, very little talks specifically about bromine. No explanation why from Delta UV.

I do not understand why both ozone and UV-C light are recommended for hot tubs using chlorine when chlorine performance declines at spa temperatures of 100F.

So, I turn my attention back to the basics for my new replacement 325 gal hot tub with 24/7 filtering. I am thinking no secondary sanitation because the design application for each individual hot tub should be specific to achieve effective results. IE ozone system designed and field tested for my specific hot tub proving no ozone reaches the water surface.

I have been told that the electrodes in salt water systems drive up the pH levels. But after reading the Chem Geek's posts, I am wondering if it is the TA.

QUESTION: If I order a salt water bromine system for my new spa and lower the TA to 80ppm (my previous target was 110ppm) will the salt water generator increase the pH or will the lower TA decrease the rate of pH increase?

For water quality and safety what is the best way to sanitize a hot tub?

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Chlorine performance does NOT decline at higher temperatures. That's absolute baloney. Kill times continue to get faster at hotter water temperatures, increasing faster than reproduction rates.

When the industry talks about chlorine not doing as well in hotter spas they are talking about how the chlorine consumption rate is faster in part due to outgassing. That is particularly true in commercial/public spas that may not use any Cyanuric Acid (CYA) in the water, but this has nothing to do with chlorine's effectiveness. It has to do with how frequently you need to dose with chlorine to maintain it's level. In a residential spa with CYA, the active chlorine level is lower so less chlorine is lost from outgassing and from chlorine oxidation of anything in the spa.

UV breaks down bromine as well as chlorine so there's not much difference there, especially with CYA in the water where the breakdown of chlorine would become slower than that of bromine. As for ozone, it does react with both chlorine and bromine but in the case of bromine it also creates more bromine from a bromide bank so the net (with a sufficient bromide bank) is that ozone generates more bromine. With chlorine, it just destroys it to chloride and chlorate. So an ozonator is worthwhile in a chlorine spa that is used every day or two because the ozone will oxidize much of the bather waste thereby lowering chlorine demand but if the spa is not used frequently then such chlorine demand is increased because ozone depletes the chlorine in between soaks.

Saltwater chlorine generators do not drive up pH directly. They produce hypochlorite then when it becomes hypochlorous acid it increases pH but then when that hypochlorous acid gets used/consumed it lowers the pH back down. What can happen is that some undissolved chlorine gas from the generator outgasses and that will raise the pH. Also the increased aeration from the hydrogen gas bubbles will increase pH from carbon dioxide outgassing. As you point out, the higher TA increases this carbon dioxide outgassing. That's why those using either bleach or a saltwater chlorine generator and maintaining a lower TA of around 50 ppm are able to have much more stable pH though they also use 50 ppm Borates for additional pH buffering to make up for the lower buffering from the lower TA level.

So yes, lower your TA, but not just to 80 ppm but to lower than that and use 50 ppm borates (most easily added from boric acid) for additional pH buffering.

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  • 3 weeks later...

No health downsides to CYA at the concentrations used in pools and spas. Of course, if one has too much CYA in the water and doesn't raise the FC level proportionately, then the active chlorine level can get too low with its obvious health consequences (i.e. inadequate disinfection). Using Dichlor-only builds up CYA which is why the spa water needs to be replaced more frequently using that method compared to Dichlor-then-bleach.

As to whether the Dichlor-then-bleach method will work well for you, it depends on your spa usage and whether you have an ozonator. If you use the spa infrequently (say only on weekends) and you have an ozonator, then you'll be having to add chlorine frequently pretty much every day which is obviously more work. If you use the spa every day or two, then adding Dichlor or bleach after a soak so that you measure a small residual (1-2 ppm) at the start of your next soak is probably not too much work.

Certainly a saltwater chlorine generator is easiest once you dial in the right level for background generation of chlorine in between soaks.

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