Another Newbie Needing Help With Water Chemistry

[DickP3]

Hello all. My wife and I have had our hot tub for about a month and are experiencing “hot tub itch.” It just started; it could be bacteria, dry skin or a sensitivity to hot water, we don’t really know.

Our tub is 450 gal with a Del MCD 50 ozonator and 40 gal/min circulation pump that run 24/7. As directed by the dealer, at startup we adjusted the pH to be around 7.2 and total alkalinity around 80 ppm. Water testing was done with Aquachek Yellow strips. (Our dealer told us to ignore the free chlorine and stabilizer pads). In addition, we were told to add ½ teaspoon Dichlor II per person after each time the tub was used. Being trusting souls, we proceeded to use the tub and add 1 teaspoon of Dichlor II after each use, usually twice a day.

Periodically during the month, we measured the pH and total Alkalinity and recorded them. About 10 days ago, I started to record the Free Chlorine and Stabilizer pad readings too. The FC has ranged from around zero to 3-5 ppm and the stablizer is 100-150 ppm. Tuesday we experienced the itch. I added one teaspoon of Dichlor II and tested the FC one hour later; it was 3 ppm. Wednesday at 3PM I added 2 teaspoons of Dichlor II; one hour later, the FC measured 3-5ppm. Thirty-one hours later, the FC was 0.5 ppm (all measurements are with the Aquachek yellow strip). The FC measured by the Aquachek strip is sort of linear with Dichlor II addition and does decline with time.

We’ve spent several days reading postings on this board and on troublefreepool.com and now realize that we need to make some changes. Probably the first step is to get a different test kit (adding 1 tsp Dichlor II to 450 gal should yield a FC of about 1.5 ppm not the 3 ppm I measured). I’m trying to decide between the TF100 and the Taylor K-2006 (which one is the better kit?)

At this point, based on having added 69 tsp of Dichlor II to date, the CYA probably is close to 100 ppm. Since it appears that we might be in the 15% of people susceptible to “the itch,” we probably should go to the “20 ppm CYA and then use bleach” method. However, our temperatures are ranging from single digits to mid 20’s and so draining the tub is not very appealing.

Sooo……, what is our best course of action for the next few weeks until the weather breaks? Should we start using bleach now recognizing that the CYA is too high and that it won’t matter what souce of chlorine we use? Or, is there some better course of action?

Thanks in advance for your help.

I'd sign my name but it keeps putting *** there.

[chem geek]

The TF100 is based on the same Taylor reagents as found in the K-2006. The TF100 kit contains items shown in this post where you can also see that the pH test uses a comparator tube found in the Taylor OTO chlorine test (becuase the TF100 includes the K-1000 OTO test kit) as shown here as opposed to the K-2006 test kit that uses a larger comparator tube for pH as shown here. The CYA test in the TF100 measures down to 20 ppm while the K-2006 CYA test measures down to 30 ppm. Overall, the TF100 is probably the better kit, though I personally like the pH test in the K-2006 and I have both (for historical reasons). You won't go wrong either way.

As for what to do now that you may have 100+ ppm CYA in the water, I would suggest switching to unscented bleach (such as 6% Clorox Regular) and target an FC when you get out of at least 10 ppm FC if not 20 ppm FC. Though that sounds really high, the CYA makes the effective disinfecting chlorine (hypochlorous acid) concentration no different than 2-4 ppm FC at 20 ppm CYA. This should be enough to kill the bacteria that causes hot tub itch, even assuming a conservative value for what it takes to kill it. If you add this bleach after your last soak of the day, then the level should be lower by the next time you get in and you probably don't have to add any more until your final soak of the day. I would not, however, let the FC drop below 5 ppm FC just to play it safe. In 450 gallons, 9 fluid ounces of 6% bleach will raise the FC by 9.6 ppm -- roughly 1 fluid ounce per 1 ppm FC.

See how the above procedure goes for you and let us know how it goes. You should remove the hot tub cover at least 5 minutes before getting in to dissipate any chlorine buildup and that should reduce any smell of chlorine.

The next time you drain/refill, just use Dichlor as a daily source and add 1 tablespoon after each soak and do this for no more than 3 days if you soak twice a day. You may find that you don't need to add a tablespoon after each soak as the chlorine demand may not be that high -- 1 tablespoon per day might be enough (in which case you do this for 6 days -- basically 6 tablespoons total). You want an FC of around 4 ppm after you add the Dichlor.

Given that you have an ozonator, I doubt that your itch is due to the bacteria that causes hot tub itch unless it grew in a biofilm stuck to some surface (because any free-floating bacteria that went through the ozonator should have been killed). Nevertheless, it will be interesting to see if improving the level of sanitation makes any difference. If nothing else, it should speed up the breakdown of ammonia so that you should measure lower Combined Chlorine and perhaps have less smell of monochloramine.

Richard

[Whoneedsavacation]

We get itchy skin when we tub frequently, especially if the sanitizer is a bit too high (we use bromine). I find that the simple expedient of applying moisturizing lotion after using the tub, especially when the air is very dry, pretty much takes care of that. "Hot tub itch" of the bacterial kind usually produces characteristic red bumps that look like mosquito bites from what I understand (never had it myself).