No Chlorine holding this winter

[kenjcom]

Hello everyone. I religiously maintain my pool chemistry, and over the last couple of weeks, my chlorine has been nonexistent. I have a 20,000 gallon pool that uses UV light and a duoclear cartridge for sanitization, so I don't need much chlorine at all. That said, I can no longer get it to register, even after dropping extra trichlor tabs and increasing the rate to max. Pool looks crystal clear, pH is and always has been on the high end at 7.7-7.8, TA is 90, CH is 375, CYA is about 65. I'm at a loss at the moment. I know organics can cause this and also high CYA, but it's winter and I haven't had anyone in my pool for two months. CYA is at the low end of high but nothing that I would think would drive this. I maintain it year round. Any ideas on getting chlorine back on scale?

 

[Mdragger88]

Regardless of your uv & whatever duo clear is you should still maintain fc above minimum for your cya level according to the FC/CYA Levels. If you do not/have not - organics will proliferate.
There are no measurable in betweens w/ cya so you always round up to the next 10.
That means for your cya is 70 = min fc 5ppm & ideally keeping it @ a target level of 8-10 ppm.
You should raise fc to target level & do an Overnight Chlorine Loss Test
If it fails it’s SLAM Process time.
Edit to add- is this a zodiac duo clear swg?
Please fill out your signature as best u can - it really helps us be more specific with advice.

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[Bperry]

Hello everyone. I religiously maintain my pool chemistry, and over the last couple of weeks, my chlorine has been nonexistent. I have a 20,000 gallon pool that uses UV light and a duoclear cartridge for sanitization, so I don't need much chlorine at all. That said, I can no longer get it to register, even after dropping extra trichlor tabs and increasing the rate to max. Pool looks crystal clear, pH is and always has been on the high end at 7.7-7.8, TA is 90, CH is 375, CYA is about 65. I'm at a loss at the moment. I know organics can cause this and also high CYA, but it's winter and I haven't had anyone in my pool for two months. CYA is at the low end of high but nothing that I would think would drive this. I maintain it year round. Any ideas on getting chlorine back on scale?

Welcome! How are you testing the water and how long have you been managing the pool? In some test kit types, chlorine can be so high it bleaches out the test reagent. But without more details that’s just a remote possibility.

The other possibilities are an algae bloom starting to grow, your UV system is degrading the free chlorine, or the sanitizer cartridge is failing.

TFP has a different process than most other pool care websites/guidance. TFP recommends not trusting any pool store testing and relying on your own personal testing with the TF-100 or the Taylor K2006C test kits. You might consider one of those if you would like to follow the TFP process.

Here’s a couple recommended reading articles.

ABC's of Pool Water Chemistry

There are several items things every pool owner should know about swimming pool water. We share details on the basics of Pool Water Chemistry.

www.troublefreepool.com

Non-Recommended Pool Chemicals

These pool chemicals should not be added to your pool. Save your money and frustration and avoid these chemicals!

www.troublefreepool.com

 

[kenjcom]

Thanks. Obviously, I have two of items not recommended in that article in that I have a UV light and a sanitizer cartridge. I do all of my own pool testing and maintenance for the past 8 years, although this current pool is only 7 months new. I updated my signature to hopefully provide some additional info.

It would be really odd that my chlorine would be high enough to bleach out the reagent because I've always maintained this pool at 1-2 ppm by adding a roughly a single chlorine tablet each week (ish).

Now that I think about it, it went from 1-2 ppm consistently and easily managed to zero pretty much after I raised my CH to its current level of 375 using the stuff from Leslie pool supply. Not sure if those are related and it may coincidence. Never had an issue like that before.

 

[HermanTX]

My thought is the operation of your UV system. Are all the lights functional? Also, do you use the mineral cartridge and if so, have you changed that periodically? With your FC at 1-2 ppm and if your UV is not functioning at full potential, then your FC can be quickly consumed by the bacteria in the water and the sun. I do not have a UV system, but I have several friends that do, and they have had to change out the unit or lights to get it working properly. You risk an algae bloom since you cannot keep your FC level at 1-2 which leads me to believe the actual UV system may be failing.

Hardness does not affect the FC level or performance.

 

[kenjcom]

My thought is the operation of your UV system. Are all the lights functional? Also, do you use the mineral cartridge and if so, have you changed that periodically? With your FC at 1-2 ppm and if your UV is not functioning at full potential, then your FC can be quickly consumed by the bacteria in the water and the sun. I do not have a UV system, but I have several friends that do, and they have had to change out the unit or lights to get it working properly. You risk an algae bloom since you cannot keep your FC level at 1-2 which leads me to believe the actual UV system may be failing.

Hardness does not affect the FC level or performance.

UV Lights are on and operational. Whether effectiveness is degrading is a fair question. Pool is crystal clear and I have no other indications that it isn't working properly. The lights are typically good for a year or so, and I'll consider changing it early if the pool condition can't be maintained.

I do use a mineral cartridge and it was changed in October (they last six months). I was aware that hardness and FC are not related, but thought maybe the chemicals I used could have impacted the chlorine.

 

[Mdragger88]

You need the fas-dpd test to turn your k-2005 kit into the recommended k-2006.

FAS/DPD Chlorine Test Kit

tftestkits.net

So you can do a SLAM Process if necessary & test fc & cc’s above 10 ppm.
Continued use of stabilized chlorine (tablets) will make your fc target to maintain sanitary water conditions increase as your cya rises.
Switching to liquid chlorine will prevent this.
Save the tablets for vacation.

How to Chlorinate Your Pool

Before chlorinating your pool, you should know these simple tips. Learn the best way to add chlorine to your pool.

www.google.com

Clear pools aren’t necessarily sanitary-
To maintain sanitary water follow the FC/CYA Levels . Whether you use uv/minerals or not.