Clarification on chlorine in spa

[bpricedo]

Hi all!

Have used this site with great success as far as the pool is concerned. Just replaced my 1998 Hot Springs Classic with a new Hot Springs Vanguard.i have read the stickies and have a few questions.

First: We use the spa often, usually every night. New spa has ozonator, Hot Springs spas have a circulation pump that runs 24 hours a day so that means ozonator is also constantly running. If I understand everything I've read, I need to add enough chlorine at night after our soak so that when we get in the next night there is around a 2ppm FC, correct?

Second: If I do leave town, I can put it into summer mode which will decrease the 24 hour circulation down to 8, I believe. This will decrease the ozonator run time and help preserve my FC. The other step is to just add a bunch of chlorine? I guess I will have to experiment to see what my daily FC loss is in summer mode to know how high I need to get the FC before I leave? What about reducing the temp as well?


I was thinking about bromine but since we do use the tub frequently and I have everything needed for chlorine I am wanting to make it work but I am worried about when I am gone for several days or a week.

 

[chem geek]

If I understand everything I've read, I need to add enough chlorine at night after our soak so that when we get in the next night there is around a 2ppm FC, correct?

Yes, that is correct. Because of your ozonator, the amount of chlorine you will need to use will probably be roughly half (or less) the "standard" amount which is 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach (3-1/2 fluid ounces of 8.25% bleach) or 7 teaspoons of non-chlorine shock (MPS, for Nature² systems) for each person-hour of soaking in a hot (104ºF) spa.

Second: If I do leave town, I can put it into summer mode which will decrease the 24 hour circulation down to 8, I believe. This will decrease the ozonator run time and help preserve my FC. The other step is to just add a bunch of chlorine? I guess I will have to experiment to see what my daily FC loss is in summer mode to know how high I need to get the FC before I leave? What about reducing the temp as well?

Yes, you should turn down your ozonator on-time as that will help a lot in having the chlorine last longer. You should then be able to raise your chlorine level to last a week, but wouldn't be able to go 2 weeks. Lower the water temperature as well since that will also help a lot in preserving the chlorine level. The following shows chlorine degradation rates at 50% per day as from an ozonator, 25% per day with no ozonator but still quite warm water, and 15% per day with no ozonator and cooler water.

DAY ... 50% .. 25% .. 15%
.. 0 ..... 10 ..... 10 ..... 10
.. 1 ....... 5 ......7.5 .... 8.5
.. 2 ..... 2.5 .... 5.6 .... 7.2
.. 3 ..... 1.3 .... 4.2 .... 6.1
.. 4 ..... 0.6 .... 3.2 .... 5.2
.. 5 ..... 0.3 .... 2.4 .... 4.4
.. 6 ..... 0.2 .... 1.8 .... 3.8
.. 7 ..... 0.1 .... 1.3 .... 3.2

As you can see, with an ozonator even with 10 ppm FC you can't go more than 2-3 days before the chlorine gets too low. Without an ozonator, you can usually go a week if the chlorine level is elevated and most especially if the water temperature is allowed to drop With a 15% per day drop, after 2 weeks 10 ppm FC drops to 1.0 ppm which is about as far as you could go though is risky in case of any blip in chlorine demand for whatever reason.

The next time you have a few days where you plan to skip using the spa, you might check your daily chlorine demand with the ozonator on full and on only 8 hours just so you can have your own baseline.

 

[bpricedo]

After reading the owners manual, summer mode stops circulation, heater and ozonator for 8 hours a day (so it still runs for 16), and will go back to regular mode if water temp drops below 80. So, I'm not sure how much use that will be during the winter.

What is a good reduction in temp for those away days? I keep it at 103 usually.

Is there a reason not to go higher than 10ppm chlorine?


Thanks for the help, it is appreciated!

 

[chem geek]

80ºF is OK and cooler is better, but people usually don't let it get below 80ºF so that they can heat it back up quickly. Also, the heat from the circulation pump in many spas often keeps it close to that temp anyway.

Higher FC will degrade the hot tub cover faster. If you don't go away often, then starting at 20 ppm FC would be OK, but with an ozonator that only buys you one extra day if the ozonator has the daily chlorine demand be 50%. If there were a way for you to temporarily disconnect your ozonator, that would be better.