Question On Bather Load

[NW_Traveler]

First, let me thank ChemGeek and Nitro for their system. I've been using it for a few months and the water has been pretty stable.

One thing I'm still struggling with is the right amount of cholorine. How many PPM does the average person use per hour? I realize the answer will depend greatly on the person - just looking for the approximate answer.

Currently I'm pouring in 5 oz of bleach before we get in. That seems like a lot though. If the hot tub is at 2ppm then 5 oz puts my 355 gallon tub up to 8.8 ppm chlorine which seems like a lot to soak in. I'm putting in 5 oz regardless of if it is one person or two. My wife complains that the tub dries out her skin. Then I usually put in an extra 2 oz after we get out for good measure.

I ran a small test last week. Me plus three young kids only took the chlorine from 6ppm to about 3ppm over an hour. I was in the full hour. The kids maybe 30 min. So, seems like 5 oz is a bit much.

My other question is on combined chlorine. I'm seeing cc of .4 to .6 pretty much all the time. Is that too much? I super chlorinate / shock to 10ppm once a week and still seeing this level of cc.

BTW, my stats if helpful:

-355 gallon tub

-99 degrees

-pH 7.5

-TA 90

-CH 160

-CYA 25

-Borate 50 (gentle spa)

Thanks,

AC

[chem geek]

AC,

The amount of chlorine needed for typical hot tub bather load is fairly independent of water volume so isn't a specific ppm since that depends on water volume. The rough rule-of-thumb is that every person-hour of soaking in a hot (100-104F) tub requires either 5 fluid ounces of 6% bleach (usually Clorox Regular which has the least amount of excess lye in it) or 3-1/2 teaspoons of Dichlor or 7 teaspoons of non-chlorine shock (43% MPS).

So if you and your wife are soaking for 30 minutes, then that's around 5 fluid ounces, but as you point out this will vary depending on the amount of sweat (children may sweat less, but may urinate more ). Most people add the chlorine after their soak rather than before, and they add enough so that they measure a small residual by the next time they soak (usually 1-2 ppm FC). That way, you don't soak in very much chlorine (so should be better for your wife) and most of it gets used up early during the soak forming monochloramine. The addition of the bulk of the chlorine after the soak then oxidizes the bather waste and avoids you having to be exposed to disinfection by-products from such oxidation. The only downside to this approach is that you don't have FC in the water during most of the soak, but unless you are soaking with someone who might expose you to a disease (i.e. person-to-person transmission), it's usually OK. Bacteria only double in population every 15-60 minutes so won't grow much during the soak and you'll kill everything off by adding the sanitizer in sufficient quantity after the soak.

After you try adding your chlorine after the soak, then measure the chlorine level before the next soak and check the CC at that time. You will probably find it to be lower than you now see. The CC will go up during your soak and when you add chlorine afterwards, but then will drop over the next hour or so and should be low by the start of your next soak. If this is not the case, then you might be using lotions or oils that break down more slowly than the urea and ammonia in your sweat and urine which get oxidized more quickly (at hot spa temperatures; urea is slow to oxidize at lower temps).

Richard

[NW_Traveler]

Thanks, Chem Geek! That makes a lot of sense. I'll give that a try.