Low Free Chlorine - Need Help Balancing Please!

casey2020

Member
Aug 28, 2020
7
Austin, TX
Hi all - I took over managing my pool from our pool company one week ago. Their “readings report” has been saying chlorine (not sure if free or combined) greater than 5 and they never test CYA. They have been using trichlor tablets weekly and occasionally liquid bleach. I know all the dangers of trichlor tablets but because I work a lot (like many folks here!) and have a 6 month old baby to keep tabs on I decided to keep the trichlor going for now. Adding bleach daily didn’t seem feasible for my schedule but I’m open to it. My free chlorine has gone down over the last week with one 3 inch trichlor tablet in the chlorinator from FC of 2, to 1.0ppm yesterday. When I got the 1.0ppm reading yesterday I added another trichlor tablet to the chlorinator and today I have these readings.

FC- 0.5ppm
pH- 7.7
TA - 110
CH - 475
CYA - 110 (it’s just below the 100 line on the cylinder)

My water is crystal clear. What is the next step to raise the chlorine? I’ve read SLAM only necessary if pool is green? Is the high CYA causing my chlorine to drop? How rapidly do I need to get the chlorine up?
Appreciate any and all help!
 

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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
21,133
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
While your FC is low your real problem is your high CYA. With a CYA of 100 you would need to get your FC up to 11-13. That is impossible to do with Trichlor tablets. Adding more trichlor tablets to try and raise your FC just adds to your CYA problem.

If you want to continue to use Trichlor instead of liquid chlorine or a SWG to chlorinate your pool then you need to plan to drain your pool every few months.

Each 8 oz Trichlor tablet raises your FC by 3.3 and adds 2 ppm to your CYA. The use of 50 tablets gets your pool to CYA 100.

You need to drain your pool about 2/3 to get your CYA to 30-40.

I suggest you read ABCs of Pool Water Chemistry and review FC/CYA Chart and Recommended Levels
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
21,133
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Ok, if I switch to liquid chlorine now do I still need to drain the pool?
You really do since it will take a lot of liquid chlorine to maintain a FC level of 11-13. You would need to be adding two gallons of 10% liquid chlorine every day. So you are needing to buy 14 jugs of chlorine a week.

And with your FC over 10 your pH testing will be unreliable.

BTW, what test kit are you using?
 

DanF

Silver Supporter
Mar 17, 2019
307
Chandler, AZ
You really do since it will take a lot of liquid chlorine to maintain a FC level of 11-13. You would need to be adding two gallons of 10% liquid chlorine every day. So you are needing to buy 14 jugs of chlorine a week.
Hi Allen - I'm not doubting you just trying to understand as I am still learning TFP methods. I get the need to maintain an FC level of 12, given the OP's CYA level of 110. I also get that it will take 2 gallons to get that pool to FC=12. But given the time of year, would daily FC consumption (due to lower UV, colder water and lower usage) be 12 ppm? I'm not questioning the OP's need to reduce CYA, but maybe doesn't need to drain right away if he/she doesn't have the time. Perhaps just replacing 1-2 ppm FC/day would be sufficient in the interim, once the pool is at FC=12?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
21,133
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Hi Allen - I'm not doubting you just trying to understand as I am still learning TFP methods. I get the need to maintain an FC level of 12, given the OP's CYA level of 110. I also get that it will take 2 gallons to get that pool to FC=12. But given the time of year, would daily FC consumption (due to lower UV, colder water and lower usage) be 12 ppm? I'm not questioning the OP's need to reduce CYA, but maybe doesn't need to drain right away if he/she doesn't have the time. Perhaps just replacing 1-2 ppm FC/day would be sufficient in the interim, once the pool is at FC=12?
How many weeks will that plan work in TX?

And you still have the problem of not being able to get good pH tests with FC over 10.

Before the weather in TX gets warm again @casey2020 needs to get the CYA down.
 
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DanF

Silver Supporter
Mar 17, 2019
307
Chandler, AZ
Ah forgot about the pH tests - I have an electronic tester so I'm not impacted by that.
And yes definitely need to get the CYA down.
 

duraleigh

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Apr 1, 2007
34,475
Sebring, Florida
I don't think you need a COMPLETE drain but perhaps about 50% should get your
CYA manageable. I would try that and go from there