Any 100% non chlorine hot tub options?
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I appreciate the effort you're making on behalf of your dad, but my ability to help you is limited for 2 reasons: you are using a hot tub, not a pool, and you're in the UK, not N. America.
I'll tell you what I can. But I have to warn you, many people find the chemistry mind-numbing and difficult. Certainly, it's far to difficult for journalists in the mass media to grasp, given the stupid stuff they constantly repeat.
1. When people speak of "chlorine in the water", as a rule, they have no idea what they mean chemically. Rather, they mean things like:
+ the pool smells sharp and chemically, and then I got itchy. When I asked, they told me it was chlorine.
+ when I use the pool, my eyes burn OR my asthma flares OR my skin itches, and I think it's the chlorine, even though I have no actual knowledge of what's in the pool.
+ etc.
2. In the simplest case, when chlorine in the form of chlorine gas, sodium hypochlorite (bleach) or calcium hypochlorite (HTH), is added to water, you end up with HOCl (hypochlorous acid) and -OCl (hypochlorite ion), plus some odd salts. NOBODY is allergic to this! If they were, they'd be allergic to the drinking water in the US and many other parts of the world . . . and that doesn't happen.
More than that "bleach baths" are a long established dermatological treatment, for both adult and pediatric patients with a variety of skin conditions, INCLUDING allergic conditions. Bleach baths involve getting into a tub filled with water containing 50 - 100 ppm of chlorine - many times higher than pools. By the way, this WILL destroy swimsuits, so it has to be done naked or in non-elastic clothes. (Google link for you to check this for yourself!)
3. Adding a person to the simple chlorine + water case complicates things, a lot. People add a lot of people goo -- skin cells, skin oils, lotions, perfumes, urine and feces. Chlorine reacts with all these to destroy them chemically, BUT it usually cannot do so quickly. Rather there's a process where the chlorine combines ("combined chlorine" is a pool trade term, but also a water treatment term) with the goo to form some complicated chlorinated organics. Then MORE chlorine reacts with those combined chlorines and EVENTUALLY breaks them down. Analyzing just what "halogenated organics" is chemically very hard work, and only recently has there been any research of high quality. (Ernest Blatchley at Purdue has done a lot of the high quality work: Google for Ernest)
4. Because the situation is so complicated and hard, even chemically or medically trained people have referred to "chlorine in the water" EVEN WHEN THEY KNEW it was not that, but much more complicated things like nitrogen trichloride, cyanogen chloride, or still more complicated stuff. There are dozens (maybe hundreds) of these complicated compounds and some of the ARE allergens and others are powerful irritants. It is ALMOST CERTAINLY these compounds that are giving your dad problems.
My older son was an elite distance swimmer in high school and he had chronic asthma, so we struggled with the effects of these compounds in my own family. BUT, he never, every had a problem on a well maintained OUTDOOR pool, even when the chlorine was so high it turned his hair ash colored (> 25 ppm).
5. On outdoor pools, exposed to sunlight (and solar UV) , this stuff is never a problem IF you maintain the pool well. Why? Chlorine alone is rather slow while dealing with this mess. But chlorine + UV is much, much faster. So if outdoor pools maintain good chlorine levels, and don't cover their pools blocking the sun, the chlorine + UV can keep up. And even though some byproducts remain, they are volatile (can become gases) and readily leave the pool . . . if it's outdoors.
6. On indoor pools this doesn't work nearly so well, for 2 reasons. First, there's no sun, and no solar UV. Second, the ventilation is usually poor (and has gotten MUCH worse in the last 20 years, due to "energy efficient" pool air systems). So, the same chlorine treatment that works just fine on outdoor pools, doesn't work nearly so well on indoor ones.
7. If you've been paying close attention, you may notice that there's a 3rd factor: how much people goo gets into the pool! Even on outdoor pools, if too many swimmers use the pool in a short period of time . . . or if too many of them pee in the pool (All elite swimmers pee in the pool -- not just US Olympian Michael Phelps!), or even if someone spills a bottle of lotion into the pool, the chlorine can 'get behind' and then the pool 'stink' starts.
You're on a farm, so you know what happens when you're burning brush, and you pile too much brush on a fire that's too small: huge clouds of smoke! This is almost identical to what happens in a pool, when you dump too much goo into a pool with not enough chlorine.
8. OK. Finally, we're at your situation -- a hot tub.
From a chlorine treatment point of view, a hot tub is the worst of all worlds:
+ There's no sun and no solar UV.
+ The hot tub is often ignored between uses so the chlorine levels are not well maintained.
+ The amount of people goo is high, compared to the gallons of water in the 'pool'.
+ The tub is usually covered, so the ventilation is terrible.
9. So, what are your options? There are a few, but please keep in mind that these are options ONLY for a hot tub NOT shared with non-family members. Most of these options are not as robust, from the point of view of sanitation, as chlorine is.
+ High levels of peroxide (~100 ppm) + UV + polyquat (2 - 6 ppm) (a particular algaecide => http://pool9.net/polyquat/ produces the most pleasant water I've every swum in. BUT it's not well tested, and you'd pretty much have to cobble it together yourself.
+ Ozone + polyquat would probably also work, but there's a problem. Ozone is even more toxic that chlorine gas, and arranging to have ENOUGH ozone to clean up the spa, but not so much that poisonous ozone gas accumulates under the spa cover is tricky.
+ PHMB + peroxide + polyquat will work IF you drain the tub regularly and replace the filter regularly. I'm not sure how it might be availble in the UK; it was patented by a British company (ICI - Imperical Chemical Industries) and sold here for years as Baquacil (an ICI Americas trademark I think). The chemical name is polyhexamethylene biguanide, also "polyhexanide", and other names. CAS #'s are 27083-27-8 or 32289-58-0 .
10. There is one other option. You can try to turn your indoor, unventilated hot tub into an OUTDOOR pool by:
a. Uncovering it regularly between uses, and
b. Chlorinating consistently, and
c. Installing a UV system to add in the missing solar UV.
11. There are some non-options:
a. Salt pool systems are just a METHOD of adding chlorine to a pool or spa: they use electricity to convert sodium chloride (NaCl) into chlorine (Cl2)
b. Bromination has most of the SAME type of problems as chlorination, but that's irrelevant, since almost all "bromine treatments" depend on the use of bromo-chloro-dimethyl hydantoin. That "chloro" is just what you might think: on a molecular level, bromine tabs have just as much chlorine as they do bromine!
12. Bottom line? There are some possible systems that will work for your dad, with or without chlorine. But they will be more expensive, and require more careful management and greater knowledge on your part.
Good luck!
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