Help with getting Chlorine Demand down

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trudge

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Jun 24, 2012
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Hi, Just got a new spa (250 gal. Aquaterra Adriana)up and running over Labor Day. I have read up on and am using the Dichlor/Bleach method. On initial fill shocked to 12 ppm with dichlor. 24 hours later FC was 5.8 ppm so Chlorine Demand baseline of 52%.

First usage had the 5.8 ppm FC to start with but 5 people soaked (2 then 3) for about 30 minutes and afterwards FC was down to 0. I shocked it to 14ppm and the next day it was down to 4.4 ppm so CD had gone up to 69%.

I have added a total of about 36 ppm dichlor over 4 days so CYA is sitting at around 30. I also tested CYA with Taylor kit and is 30.

I have switched to bleach at this point. Shocked to 10.4 last night and today FC is 2.6 so CD is 75%. How do I get my CD down to a lower value? My numbers are pH-7.5, TA 60, CH-120. I have boric acid but have not added it yet. I am wondering if that would help.

The tub does have an ozonator which I am wondering if that is part of the issue although it is only on for 1 hour for first filter cycle and then 30 minutes 12 hours later for the second filter cycle.

Any input would be appreciated.
 
In a clean tub, ozone and chlorine will annihilate one another although most hot tub ozone generators are pretty weak and inefficient.

Let me ask you this - did you purge the hot tub with Ahh-Some (look it up online or here on TFP) BEFORE you filled it??

Even brand new hot tubs need to be purged as they are often filled with water at the factor for leak and pressure testing and then shipped out with moisture left in the plumbing not to mention various greases and other manufacturing residues. All of this leaves behind a good deal of organic junk for chlorine to react with.
 
Thanks for the suggestion of Ahh-some. I just ordered some. I just am wondering why the CD is climbing like it is. I did that initial shock of 12 ppm with dichlor and the CD was 52% which is not too bad. It does seem to have topped out at 75% because my latest CD is 71%. I will shock to 10 again and see if it keeps dropping. I am going to change the water in 3 weeks since this is my initial run and will use the Ahh-some then unless I start having issues. Any thoughts on adding the 50ppm of borates? Would this help things out?
 
trudge said:
Thanks for the suggestion of Ahh-some. I just ordered some. I just am wondering why the CD is climbing like it is. I did that initial shock of 12 ppm with dichlor and the CD was 52% which is not too bad. It does seem to have topped out at 75% because my latest CD is 71%. I will shock to 10 again and see if it keeps dropping. I am going to change the water in 3 weeks since this is my initial run and will use the Ahh-some then unless I start having issues. Any thoughts on adding the 50ppm of borates? Would this help things out?
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Borates are for pH control , I doubt it will help with chlorine demand. Chlorine demand comes directly from the oxidation of bather waste and sanitation. If your chlorine demand is high, then you likely have something in your plumbing causing it. Unless water is expensive where you are, then I’d purge the tub and dump the water as soon as your Ahh-some arrives.
 
Well I think I may have shocked the spa enough to get my CD down to a better level. A day ago it was down to 62%. Tonight it was 13% which seems a bit low but it went from 3.2 to 2.8 so that's what the numbers work out to. Maybe with the shocking and not soaking last night there wasn't much demand. I got the Ahhsome today but I will wait to use it at the one month drain and fill if CD stays at a good level.
 
Don't know what I was doing on my 13% calculation but that was wrong. Actually calculated to around 50% CD. CD has consistently dropped to where I am getting to a healthy level. I am going to run the Ahh-some through in 2 weeks since that will be one month since initial fill. Dichlor/bleach seems to be working well. pH has been stable although it did drop some after MPS shock.
 
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