Chlorine consumption per bather

[Daf-Tekno]

Hi TFP,

I'm sure I read this in another thread somewhere, but for the life of me I can't find it!
And searching doesn't seem to give any usable results.

Can anyone tell me how much chlorine 1 bather consumes in a spa over a given time period?
(Jacuzzi Calgary told me 1 person uses 1 ppm every 15 minutes, though it's been a long time since I trusted anything they've said...)

Thanks - D

 

[JasonLion]

The rule of thumb I have heard is 5 fluid oz of 6% bleach (or the equivalent) per person/hour. Actual usage varies somewhat depending on many factors, this is just a typical/average number.

You don't measure in ppm, because chlorine usage per person/hour is an absolute amount, while 1 ppm varies with the tub size.

 

[chem geek]

For a hot (104ºF) spa it's roughly 9 grams of chlorine (in weight Cl₂) per person-hour which translates to 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach or 3-1/2 fluid ounces of 8.25% bleach or 7 teaspoons of non-chlorine shock (43% MPS -- a disinfectant only with silver ions as with Nature²). In 350 gallons, which is a typical spa size, this is 6.8 ppm FC so every 15 minutes that would be 1.7 ppm FC. So the rule of thumb you were given was either for a larger 600 gallon spa or they somewhat under-estimated.

It's a rule-of-thumb anyway and depends on the cleanliness of the bather, their size, how much they usually sweat, water temperature, etc. The real rule you should use is to add whatever amount of chlorine is necessary after a soak so that you still measure at least a small residual of chlorine for the start of your next soak. You should never let the chlorine level get to zero (or near-zero), certainly not for more than an hour or so.

 

[jweaks]

Is it simple math at that point for 6% bleach post-bathing dose?

If it's 5 fl oz per bather per hour, does that mean 2.5 fl oz per bather per half hour?
So for me and my wife for half an hour it's 5 fl oz we know we need to put back in when we're done?
If our teen joins and it's the three of us for 15 minute it's 3.75 fl oz (=1.25 * 3)?

Our typical soak is about 20 minutes. Just trying to get a ballpark typical minimum dose I can do for our 350gallon spa.

 

[A.O.]

As chem geek said you want to add enough after a soak so you still have some in the tub when you go to your next soak. I have a 450 gal tub I use twice a day for 15-30 minutes each time, normally I add about 2 - 2 1/2 oz of 10 % chlorine to get that job done... Play with it for a while and you will figure out what you need.