I Need A New Method To Sanitize My Hot Tub

[RelaxedinMissouri]

We have a 419 gal. Bullfrog. For over three years we have been able to keep our tub perfectly balanced (rarely have to even do a test) using the muratic acid, bromine bank and Clorox sanitizer process. It remains stable and we clean/drain every 4 months like clockwork.

I’m going to make a long story short: after a visit to my doctor (BTW I am female) he informed me I have contact dermatitis, presenting as the most intense itching you can imagine. I have NO visible rash. This has been getting worse and more persistent over the past, umm THREE YEARS which is why I finally sought medical help (I thought it was hormones. It is NOT.)

After ruling out everything one-by-one, the hammer comes down on the Clorox. That was pretty much confirmed when I swam in my brothers pool last weekend and a few hours later the intense itching started again [after staying out of my tub for two full weeks and NO ITCHING!] So chemically speaking, Clorox is what the pool and the hot tub have in common (I think).

What are my options? I don’t understand what Dichlor is or if that would work for me. What about a salt water method?

The tub is used by myself and my husband, 3-5x per week. I currently use a spa frog with bromine.

I’d appreciate any insight or advice. I’m going to do whatever needed so I can get back in my tub… I sure miss it! Also, if I switch up methods, I’ll most likely need a new test kit? I’m using the Taylor bromine kit.

Thanks,

Kelley

[chem geek]

You may have sensitivity to halogens in general so both chlorine and bromine. If you think it's only chlorine, then you can try oxidizing your bromide to bromine by using another non-chlorine oxidizer such as non-chlorine shock (MPS) though some people have sensitivity specifically to it.

If you had a sufficient bromide bank and you waited a bit after adding chlorine before entering the spa, then it's unlikely there was any chlorine left when you went in because chlorine converts bromide to bromine rather quickly and the chlorine gets consumed (it becomes chloride salt).

As for Dichlor, it produces chlorine though the Cyanuric Acid (CYA) with it will moderates chlorine strength. As for a salt water system, it just generates chlorine or bromine depending on the salt in your spa.

The only residual chemical specific to Clorox bleach is sodium polyacrylate. So it's more likely to be a reaction to halogens, both chlorine and bromine. Your doctor could do a patch test to be more definitive.

[KyleCT]

I agree with "Wizard of Water" use bromine and Non-chlorine shock or MPS Activator, in my the best combo our there.

[dlleno]

its interesting how some bathers are sensitive to CL but not to Bromine. i would only like to add here that the behavior of the oxidizer in the presence of sodium bromide is subtle. that is, and chem geek needs to chime in here with applicable additions and corrections, my understanding is that a relatively short time elapses from the time the oxidizer is added to the point in time when the bromine conversion is complete. This is assuming there is sufficient bromine bank of course. After that short period of time has elapsed, the bromine conversion is complete and all oxidizers are equal in the sense that they have performed their work to convert the bromide bank, which means they are no longer behaving natively as MPS, chlorine, etc.

The two step bromine plan is really quite good, and yes I have also used straight MPS as the oxidizer and like it alot, as during the conversion you don't have any chlorine smell at all; I just note that during or before the conversion is complete, there are some advantages to using chlorine, so I like to alternate. my primary oxidizer is dichlor which I like because of its downward pH influence, but then I use MPS from time to time like once per week.

[chem geek]

Yes, chlorine oxidizes bromide to bromine rather quickly. Ozone does it more slowly and MPS even more slowly.

MPS is net acidic, more so than even Dichlor.

[dlleno]

Thanks what kind of times are we talking about for the conversion? seconds, minutes?

[chem geek]

The paper in this link gives the rate of reaction of chlorine oxidizing bromide to bromine. It looks like it's roughly a conversion of 4% of the bromide every minute when the FC/CYA ratio is 10%, but that's at cooler temperatures (i.e. 77ºF). At 95ºC it would likely be about double the rate plus the HOCl concentration is nearly triple so net that's 24% per minute. So figure the conversion is mostly done within 10 minutes.

[dlleno]

great info! thats important to know that before 10 minutes elapses you have a partial chlorine and bromine spa. but if you switch to bleach at CYA=50ppm (or earlier) and you dose to FC of about 2-3ppm that would represent lower than 10% FC/CYA ratio right? would that tend to increase the rate of conversion?

also -- what can be said about speed of the MPS conversion -- is it like 2x or 3x or 10x that of chlorine?

[chem geek]

Yes, your numbers are lower than the 10% I assumed so would be proportionately slower -- figure twice as long.

MPS oxidizes bromide to bromine the most slowly (ozone is in between in its speed). I don't have actual rate numbers for MPS but was told by Dupont that it is slow which is why MPS in a bromine spa will tend to have the MPS oxidize bather waste first.

[dlleno]

so lower than 10% FC/CYA slows the conversion? why is that? what if you had no CYA present at all -- you oxidized with bleach on the first fill?

[chem geek]

The active chlorine (hypochlorous acid) level is proportional to the FC/CYA ratio. This is because CYA is a hypochlorous acid buffer. So if the FC/CYA ratio is lower then there is a lower hypochlorous acid concentration so slower chlorine reactions.

If you had no CYA at all then the hypochorous acid level would be much higher and therefore much faster. It will be limited from hypochlorite sources by the pH rise, but it will still be much higher than with no CYA. So high that if kept longer-term it would damage spa components such as degrading hot tub covers faster. This is one reason the industry says never to use bleach. That's simpler than having to explain the full reason which is not to use only bleach and instead make sure there is some CYA in the water.

[dlleno]

(sorry for the mis-fire this post was unintentional)

[dlleno]

nice info thanks. These are slower conversions than I thought. what is interesting is that near the beginning of the water life, the FC/CYA ratio is high (if you are adding straight dichlor. no tabs), such that the conversion to bromine would happen rapidly. About half way through the journey towards 50ppm CYA you will pass the point where the FC/CYA ratio is 10% (say, 3ppm FC and 30ppm CYA). From that point on the conversion will take more than 10 minutes and by the time you reach 50-60ppm CYA the conversion will take 20-ish minutes.

Even more interesting is that if the MPS conversion is even slower (lets assume twice as long) then those who are sensitive to MPS would not want to enter the spa for about an hour or so after dosing.

in my particular bromine plan (posted a long time ago) The calculator website told me that 7 oz of dichlor in 500 gallons would result in 53ppm CYA, so I set that much (or about 1 cup) dichlor aside when I drain and refill -- then, when that is all used up I switch to bleach.