Should I smell bromine on my skin when I get out of hot tub, is that normal?

Bromine is popular with hot tubs because it doesn't have a smell like chlorine does. When chlorine kills, it creates a chloramine. When this chloramine gets oxidized (using shock) it creates the chlorine gas that you smell. Bromine doesn't do this, therefore it doesn't have a smell. However, if you are concerned with this, I would suggest switching to a better brand of Bromine.

Shocking chloramines doesn't create chlorine gas.

From Wikipedia



So what I am saying is that when oxidize (superchlorinate, shock) the chloramine, it turns into a gas that you can smell.

I think this needs a little clarification... When there is insufficient amount of chlorine (FC) in the water you have a tendency to generate Chloramines (combined chlorine), which does smell. Shocking will destroy the Chloramines and result in only FC which does not have a strong smell in the low quantities used in pools and hot tubs.

As far as Bromine smell mentioned in the original post, Bromine does have a strong smell. Here is an quote from a posting by WaterBear:

"It has a harsh smell (chemical or caustic is how it is often described) and is a known sensitizer that many people have an allergic reaction to."

May try opening up the hot tub cover to air it out for a few minutes prior to entering. Sometimes when I get in I get a stronger odor if I just lift the cover and jump in.

Bromine smells different than chlorine; some people prefer one over the other. Bromine most definitely forms bromamine and these also smell, though different than chloramines and much less offensive than the worst of the chloramines. Bromamine is still an effective sanitizer (technically, it's the monobromammonium ion, NH₃Br⁺ which is in equilibrium with monobromamine, NH₂Br) while chloramine is not an effective sanitizer. When you get out of a pool or tub, both bromine and chlorine will continue to oxidize ammonia in sweat and form bromamine or chloramines. That is normal, though the smell should be faint.

As for the relationship of chlorine, chloramines, shocking and smell, what can happen is the following. If you don't use enough chlorine, then the Free Chlorine (FC) can run out and whatever ammonia was present in the water before this happens would have combined with FC to form monochloramine. Though monochloramine smells, it takes quite a lot to noticeably smell bad. If you continue to soak or swim, then you continue to add ammonia to the water and without any FC it builds up. If you then shock the water with a high FC level, you then form lots of monochloramine, but also form dichloramine which smells worse and also form nitrogen trichloride which is the most volatile, smelly and irritating of them all. This is why it is far better to always have sufficient FC in the water to continually oxidize bather waste so that the more obnoxious chloramines don't form in offensive quantities.

There is also some subtlety to the above with respect to Cyanuric Acid (CYA) levels. In pools with very high CYA levels, the oxidation of bather waste slows down unless the FC is proportionately raised higher. This can build up monochloramine to higher levels. At the other extreme with no CYA in the water at all as with many indoor commercial/public pools, the higher active chlorine level forms more nitrogen trichloride and is mostly what is associated with bad pool smell as well as irritation at such facilities.

By the way, the Wikipedia article is wrong because it is not ammonia that gets outgassed, but nitrogen gas. The primary result of oxidizing ammonia with chlorine is nitrogen gas. Some nitrate ion is formed as well and remains in the water. To the extent that chloramines form, some may outgas, most especially nitrogen trichloride which is the most volatile. Also, the process does not take 24 hours. With no CYA, the oxidation of 1 ppm monochloramine (measured as ppm Cl₂ such as Combined Chlorine, CC; if measured as ppm N then this would be 0.2 ppm) by using 10 ppm FC is 90% complete in 2 minutes and 99% complete in 4 minutes at 77ºF. In a pool where you go to shock level of an FC that is 40% of the CYA level which is equivalent to around 0.6 ppm FC with no CYA, it takes 45 minutes for 90% completion and 87 minutes for 99% completion (actually faster since pool water is typically warmer than 77ºF). As for removing the FC, if there is no CYA in the water than bright sunlight near noon for 4 hours in a shallow bucket at a pH of 7.5 would remove over 99% of the chlorine. In a pool with CYA, it would take far longer, but then one wouldn't want to remove the FC completely (i.e. the Wikipedia article is about removing chloramines for aquariums).

Gotta love the Geek.

Scott

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