Chlorine isn't working!

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tbamy

tbamy

Active member
Apr 30, 2022
26
Sacramento
Pool Size
23000
Surface
Plaster
Chlorine
Liquid Chlorine
Over the last few weeks, I've noticed that my liquid chlorine isn't lasting as long as I would expect. Last summer, I needed to add 1 gallon of chlorine every 2-3 days, depending on how sunny it is. But this May, I've been going through 10-12 gallons a week! I don't have any visible algae, but I thought I must have some sneaky secret algae somewhere, so I decided to do a SLAM. Based on my CYA (48) I believe my target FC should be 20+. This morning (4 hours ago) I added 4 gallons of 10% chlorine, plus a half-gallon of 12.5% chlorine. Just tested, and my chlorine level is 9ppm. Last year, I calculated that 1 gallon of chlorine (10%) would raise my FC levels by 6-7ppm. So I would have expected it to be raised up to at least 25ppm.
My newest guess is that the chlorine is bad. I've been buying it from Walmart. Does this sound possible? Does anyone have any other theories for me to work with? I'm going to keep adding more chlorine and trying to get the levels up, as well as running the filter and the vaccuum. Again, there is absolutely 0 visible algae. This is getting ridiculous!

Thanks in advance for your input.
 
How are you testing? You signature shows "TF-100 test kits have been ordered just waiting to receive them"
 
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tbamy said:
Last year, I calculated that 1 gallon of chlorine (10%) would raise my FC levels by 6-7ppm.
Click to expand...

Your calculation was off by a factor of two, if the pool size in your signature is correct.

One gallon of 10% will raise FC in your 28,000 gallon pool by around 3.5 PPM. So four gallons of brand-new 10% plus 1 gallon of brand-new 12.5% would have raised your FC by around 18 PPM. If the chlorine was old, it would have raised FC by less.
 
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DrewLG said:
Your calculation was off by a factor of two, if the pool size in your signature is correct.

One gallon of 10% will raise FC in your 28,000 gallon pool by around 3.5 PPM. So four gallons of brand-new 10% plus 1 gallon of brand-new 12.5% would have raised your FC by around 18 PPM. If the chlorine was old, it would have raised FC by less.
Click to expand...
that's helpful, thank you. I'm doing my calculations by hand in a notebook so math errors do happen. it sounds like you agree that the chlorine might be old?
 
Update:
I tested my chlorine at 8pm (filter is running 24/7; the last time I added chlorine was 5pm) and my FC was 25.5ppm. I tested again just now at 11pm, and my FC is 18ppm. I lost 7.5ppm in the dark. I've added 9.5 gallons of chlorine TODAY and I reached SLAM level for a few hours but I'm below it again. This is so frustrating! I have brushed the entire pool and run the vaccum many times today. I've cleaned out the cartridge filters. The water is clear! Argh! I can't keep spending $50/day on chlorine. Help! I'm off to add a few more gallons...
 
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If you lost 7.5ppm in 3 hours 8pm-11pm 25.5ppm-18ppm but last added chlorine at 5pm you must have been shooting way over target FC for 50cya at the 5pm chlorine addition.

Are you trying to hit and maintain 20ppm of FC for a SLAM or are you trying to do something else?
 

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RookiePick said:
If you lost 7.5ppm in 3 hours 8pm-11pm 25.5ppm-18ppm but last added chlorine at 5pm you must have been shooting way over target FC for 50cya at the 5pm chlorine addition.

Are you trying to hit and maintain 20ppm of FC for a SLAM or are you trying to do something else?
Click to expand...
I'm trying to hit and maintain 20ppm FC for a SLAM.
 
Here's my AM update:
This morning 6:30am, I'm getting a FC level of 20.5ppm. That's a loss of 5ppm overnight, and I don't know how to make sense of the 18ppm reading yesterday evening. As suggested by other comments, I'm going to get the PoolMath app today, and I'm also going to check the date on my chlorine.
 
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Algae is hiding somewhere if the pool is clear and you’re going through that much FC in the dark.

Checked any light niches? Skimmer throats? Weir doors? Ladders?
 
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