UV Sanitizer and Bromine Demand

[Lebsc]

Hi all,

I've been using the website as a great resource in balancing my hot tub water chemistry but have never posted. I'm using the Brilliance chlorine free bromine system that consists of the sodium bromide startup coupled with a bromine only floater and an oxidizer. My tub also has an ozone generator and UV light sanitizer. I'd been having difficulty keeping my bromine levels up. I'd oxidize after use per chemgeek's recommendations and the levels would shoot up past 10ppm but within a day or two they'd fall back down in the 2-4ppm range and often within 3 days it be at .5ppm using the Taylor bromine fas-dpd kit. I adjusted my floater upward - the Brilliance manual said a level of 2-2.5 was recommended for my size tub (355 gallon) but I'd have it set on 7 or 8 and still the levels wouldn't stay up for more than a few days. I couldn't figure out why but read a few posts regarding depletion of bromine by UV. I begun to think that my UV sanitizer was cannibalizing my bromine levels so I did a little experiment and unplugged the UV sanitation light (which runs 24/7 and has water circulating over it 24/7 by virtue of the recirculation pump). It's been 3 days and my bromine levels have stayed in the 5-6ppm range. I've been ratcheting my floater down from 6 and is now on 2 in hopes of taking my bromine levels down below 4. Thought people might find this useful if they're facing a similar problem

 

[chem geek]

Welcome to TFP!

The ozone will create more bromine from the bromide bank but will also deplete some going to bromate (most goes to bromide to be used again). With your bromine floater, it should be able to replenish the bromide that got lost to bromate from the ozonator. So most spas using bromine and an ozonator are able to work well.

I thought that UV would deplete bromine to bromide and not bromate so the only way that would be a problem would be if it were too powerful such that the ozonator is not able to produce bromine faster than the UV is destroying it. Your experiment is exactly what I would have suggested you do so you've confirmed my suspicions. Thanks for reporting in.

This situation should be read by anyone considering using a UV system in a spa, especially a UV system that is oversized or run too long. Usually for a bromine spa, an ozonator works well, but there's really no need for using UV.

 

[Lebsc]

Thanks, Chemgeek. I can't thank you enough - my little experiment was a direct result of pouring over dozens of your historical posts trying to get my water situation squared away. I had everything down to textbook - including the Ahhsome flush on my brand new spa - and still couldn't figure out why the bromine levels would drop from 10 to almost zero PPM after 48hrs without any use. My confusion was compounded by the fact i have an ozone system which should theoretically serve to reconvert my bromide bank into useable bromine. Finally i came across a series of posts where a dealer was having issues keeping his chlorine levels up with a new tub with a UV sanitation system that had been upsized by the manufacturer compared to prior model years. I coupled that tidbit with the knowledge that bromine and outdoor pools don't play well together due, in part, to UV degradation. Low and behold the uv sanitizer in my spa must be either oversize or the fact it runs 24/7 alongside my recirc pump results in a rapid degradation of bromine levels. I'll repost my results in the coming weeks but am hopefuls I've discovered my bromine hog. Unfortunately it evidently happens to be a sanitation system the manufacturer is quite fond off.

chemgeek- do you think it's worthwhile installing a timer to allow the UV system to run for a set period of time each day as opposed to disabling it in its entirety?

 

[chem geek]

I don't see any value to the UV system, especially since you also have an ozonator. Ozone will help to oxidize bather waste wile UV doesn't do as good a job with that -- it breaks apart some molecules but doesn't oxidize them as thoroughly. With ozone, you not only get ozone for some additional disinfection against more chlorine-resistant pathogens such as Crypto (as unlikely as that will be in your spa), but ozone breaks down into hydroxyl radicals (among other things) and those are very powerful oxidizers. UV by itself doesn't do that. The only purpose for UV would be if you didn't have ozone and needed to control chloramines or Crypto, but with ozone you shouldn't need the UV at all.

 

[Lebsc]

It's been a couple of weeks since I disconnected the UV system and thought I'd provide an update. I'm 100% confident my excessive bromine demand was caused by the UV light. I now get bromine levels for 3-4 days in the 4-5ppm range after adding only 1/2 oz of MSP after a soak when used in conjunction with my ozone generator. That amount would be depleted within a day when the UV system was running. Hope this information helps others trying to figure out why they have high bromine demand in a tub that utilizes a UV light.

 

[chem geek]

Thanks for the feedback. We know that UV will deplete both chlorine and bromine, but good to know that this happens in real-world situations in spas. We've seen this before with chlorine, but your situation confirms that the same problem occurs with bromine as well.