chlorine can ruin your hot tub???

[NurseN2000]

I did not know this, but that is what the girl at the local dealer (not where I purchased my tub, just a nearby pool & spa supply store) told me, when I told her I didn't want to use the more expensive bromine with the smell I don't really like.  I told her hmm, I'll take the chlorine anyway, thank you .  I'll take my chances lol. 

[Dr. Spa™ Ret.]

Those bromine tablets contain up to 60% chlorine.

[TwinCitiesHotSpring]

chlorine can ruin your hot tub? hmmm...what kind of chlorine? pucks, granular, liquid, gas? in what amounts? what if I keep my chlorine level at 1-2ppm, will that ruin my tub? and how exactly will it? does is break down the sch 40 pvc?  just a few of the questions I would have asked her   but no really this must have been a part-time college kid or something because that statement is that flat out ridiculous and does not even warrant a serious reply...

[NurseN2000]

You hit the nail on the head Twin, definitely a part time college girl...and hopefully not a chemistry major!!

[hottubdan]

Highly acidic chlorine tabs can ruin hot tub.  Granular is what you want.

[Waterbug]

Water can ruin your hot tub too, if you let it freeze.

[Water Boy]

Highly acidic chlorine tabs can ruin hot tub.  Granular is what you want.

Bingo! In fact, most manufactures will void the warranty if chlorine tabs are used in the spa. So, I guess she was at least somewhat right.

[NurseN2000]

I think she was referring to the granulated dichlor I had in my hand, since I was nowhere near the trichlor tabs they sell in the pool section lol...but you're right, I guess there was some merit to what she said 

[d00nut]

calcium hypochlorite isn't something that you'd want to put in your hot tub either. Dichlor is king

[chem geek]

Actually, Dichlor (or other source of Cyanuric Acid, CYA) initially and then bleach is king.  The following are chemical facts independent of concentration of product or of pool or spa size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

Trichlor is very acidic, but if a strong pH buffer is used then it can be managed.  After all, that is what the AquaFinesse system does with their Spa Tabs which is Trichlor.  Some hot tub manufacturers void their warranty if Trichlor is used.

However, the continued use of Trichlor or Dichlor results in an increasing CYA level and this lowers chlorine effectiveness slowing kill times for pathogens and oxidation rates for handling bather waste.

Cal-Hypo increases CH over time and that increases the risk of scaling unless you start out with a very low CH level or keep the pH and TA very low.

If you initially add CYA, such as using Dichlor for a week or two, and then switch over to using bleach, then you do not build up either CYA nor CH and can generally have the water last twice as long between water changes (one can use Dichlor for one day per month to maintain the CYA level which otherwise slowly drops from oxidation by chlorine).  One needs to manage the pH more carefully by using a much lower TA level (usually around 50 ppm) and use additional pH buffering such as from 50 ppm Borates (found in ProTeam Gentle Spa, for example).

Most people use Dichlor and are happy with it, but Dichlor-then-bleach has the water stay clearer longer.

[NurseN2000]

Thank you for the information Chem, much appreciated!  My test strips measure for water hardness, but not CYA, is that something I should be measuring?  Does anyone else measure this?  I really don't want another number to chase if I don't need to, I'm just getting a handle on the TA, pH & chlorine as it is lol.

Does anyone else use bleach in their routine?  Sounds like an incredible cost saver... are there any cons to it's use in a hot tub? 

[chem geek]

Most people use Dichlor and test strips and just deal with having to change the water sooner then they would otherwise need to do and pay more than they need to but like the convenience of Dichlor being net acidic (when accounting for chlorine usage/consumption which is acidic) so that their pH tends to be automatically maintained (though over time they need to raise the TA using baking soda).  However, there are quite a few people who use the Dichlor-then-bleach method successfully though it is certainly not conventional.  Because one needs to get the TA substantially lower (usually to 50 ppm or even somewhat lower), it is best to measure it accurately where the best test kit is the Taylor K-2006 or the TFTestkits TF-100 (or the TFTestkits TF-50 if one already has a drop-based pH test).  If you don't get a test kit with a CYA test, you can just approximate the CYA level knowing that for every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.  Also, about every month in a hot spa, the CYA will drop by about 5 ppm so will need replenishment by switching back to Dichlor for a day or two.

You can read more about the Dichlor-then-bleach method in this post, but I would recommend getting the TA down to 50 ppm, not 80 ppm as indicated in the post.  I would also use 50 ppm Borates, such as from Proteam Gentle Spa -- this should not be optional.  By doing these two things, you will make it far less likely for the pH to rise too quickly over time.  If one doesn't do these things, then one can get scaling which is very detrimental in a spa.  This makes this method riskier for those who don't set things up properly initially and is one reason this isn't normally recommended (another is that it isn't profitable for spa stores and another is that people can splash bleach on their clothes if they are not careful while spilling Dichlor powder is less likely).  Also, I don't think that MPS is needed -- most people just use chlorine alone and have no need for either non-chlorine shock nor for clarifiers.  Finally, the water is changed at roughly double the standard Water Replacement Interval (WRI), not just after 6 months.  So the time depends on your bather load.  The standard WRI = (1/3) x (Size of Spa in U.S. Gallons) / (# of bathers) where the soak time is assumed to be around 20 minutes.  So the extended WRI for the Dichlor-then-bleach method and using person-hours is (2/9) x (Size of Spa in U.S. Gallons) / (Daily Person-Hours of Soak Time).  So if there is just one person soaking for 30 minutes once a week in a 350 gallon spa then this is (2/9)x(350)/((30/60)/7) = 1089 days (so basically much longer than even once a year).  If there are two people soaking for one hour every day, then this is (2/9)x(350)/(2) = 39 days.  So the bather load makes a huge difference in how long the water will last (and in how much chlorine you will use).