Can't figure out my salt water hot tub chlorine levels

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Jul 15, 2013
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I've been having quite a bit of issues maintaining the chlorine level. It's an 8 x 10 rectangle that I run for 3 hours on 2100 rpm every day. I've been keeping the chlorinator at 60%. Salt level ranges between 2200 and 2900. I just added about half a bag of salt when it got to 2000 and now it is at 3800.
When I test the chlorine, the first two drops turn it orange.
I've had this happen before but it was after I added some liquid shock because the water started to look like it had some color to it. It eventually drops back to no chlorine. (Maybe 2-3 weeks)
So what am I doing wrong to cause such chlorine Spikes?
I'm sure I'm missing something but for my first year with the pool and hot tub, I had no issues during the summer!
Now that it's just the hot tub, I am feeling like the rookie I am.

I added a cover in the fall too, but I can't imagine that has an impact.

Thanks for the help as always!
 
What kind of test kit are you using? Sounds like the OTO chlorine test and not the recommended FAS-DPD chlorine test.

Sounds like your FC is rising a LOT, which could happen if the tub is covered and you are not using it very often. The SWG is just going to keep making chlorine every day, even if you do not need it due to losses.

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Thank you Jason. I'm in Massachusetts. I did the chlorine test with the tf-100 on the last time it was orange, but I forgot the results. I'll test the correct way tomorrow and report my results.
 
Higher salt levels will have the saltwater chlorine generator output more chlorine. Also, if you have periods of no use of the tub then the chlorine level will build up if you had the chlorine generator set to output a level that handled some bather load.
 
If the chlorine level is too high you should first turn down the chlorine generator so that it doesn't keep producing too much chlorine. You could turn it off if you remember to turn it back on once the chlorine level drops. With no ozonator, if the spa is kept hot then you should have 20-25% FC drop over 24-hours with no bather load. If you have an ozonator, the FC may drop by 50% or more over 24-hours. That's the easiest way to lower the chlorine level. If you have to lower it faster, then adding 3/4 fluid ounce of 3% hydrogen peroxide to 350 gallons will lower the FC by 1 ppm so you can scale that up accordingly once you know the accurate FC level using a FAS-DPD chlorine test kit (not the OTO one you used).
 
Using the tf-100 I got a chlorine level of 67ppm. Just a bit high, I would say. :(
The only question I have is the kit was kept in the pool house and it froze. Do I need to replace the chemicals? Do you think it's accurate still?
 

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pwrstrk said:
If your chemicals froze I would toss them and order new ones.
Click to expand...
I cut my sample in half with no chlorine tap water which I tested prior to the test and my ppm came up to 75 ppm. So I think something is up with them.
I had turned the SWG off when I tested yesterday and I opened up the top. It's going down to 10 degrees tonight so I'll reopen it tomorrow when it warms up and its sunny out.
 
I received the new chemicals and did the test twicestwice to determine accuracy.
TA = 60
TC = 70 ppm
FC = 67 ppm
CC = 3 ppm
CYA = clear. Never turned cloudy

Thoughts?

Edit....I added 64oz of 3% hydrogen peroxide. 1000 gal tub. I should see a drop in FC by about 26 if the pool math is correct.
 
Turn off the SWG until the FC level comes down.

One important thing to keep in mind about hot tubs with SWGs is that chlorine production is uniform over time, while chlorine demand varies dramatically depending on how often you use the spa. It is very very easy to build up very high FC levels when you are not using the tub regularly. These very high FC levels will damage the tub, especially if the CYA level is near zero. With CYA at zero, it is critical that you not let the FC level get that high. If you can't get this completely under control right away, it would be a good idea to raise the CYA level to around 20 to help mitigate the risks of high FC levels.
 
JasonLion said:
Skip the hydrogen peroxide as well until levels come down.
Click to expand...

Huh? ChemGeek above and all over the interwebs say to lower the FC quickly, use 1 cup to 350 gallons to lower the FC by 10 ppm.

Why do you suggest I skip the Hydrogen Peroxide now? Not that I can take it out, but to hold off on adding any more?

Just trying to add up the facts here. Thanks for your help!

BQ
 
If you added some Cyanuric Acid to the tub then that would significantly cut down chlorine's strength and is something you'd need to add anyway. The chlorine level would usually drop by 20-25% every 24 hours in a hot tub and if there is an ozonator it will drop even faster at 50% or more. The damage from one day or two is negligible. What Jason was referring to in terms of damage was what would happen if you maintained such high FC levels (especially with no CYA) for an extended period of time.

And yes, if you want to drop your FC level faster you can use hydrogen peroxide for that though it would be extra cost. You could certainly see what happens to the FC level with the spa uncovered after 24 hours. If the level isn't dropping fast enough then you could get the hydrogen peroxide.
 

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