Unable to keep chlorine in the pool

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  • Last Post 05 July 2021
94tbird posted this 04 July 2021

Hey guys, long time lurker first time poster.  This is only my second season owning a pool.  Last year I had the water balanced all season and it was always simple and easy.  This year I have everything balanced, ph, cya, Ch, Alk, EXCEPT I cannot keep chlorine in the pool.  I have an in line chlorinator directly in line in the return line to the pool, no black hoses, last year set to 3.5, this year set to full and I am always about 0.5 FCL, with the TCL always matching or within   . 1 of the FCL.  I have been tested for phosphates and they are low, under 100ppm, and have been tested for nitrates and there are none.  The water is crystal clear, no visible algea anywhere.   If I shock the pool the FCL will come up but it's gone back to 0.5 within a day or two.  I do not have a lot of sun on the pool at any point during the day. 

 

I'm at a loss here and so are the pool stores in my area.  One major chain keeps telling me to add 1lbs of shock which clearly doesn't work.  The other mom and pop store suggested I slam the pool so I put in 6lbs of 70 percent chlorine shock.  It raised it to over 10ppm, I'm not sure how high as the tester only goes that high before it just says high.  It took just over 24 hours to drop below 10ppm, and at 26.5 hours I'm at 8.68ppm.

 

Latest water test before I did slam, my test on left, Leslie's on right

Fcl 0.40. Leslie's 0.31

Tcl 0.79.leslies 0.31

Ph 7.1. Leslies 6.7

Alk 113. Leslie's 81

Ch 52. Leslie's 266 - I belive my reagent is expired 

Cya 59. Leslie's 79

 

 

Anypne have any insight here? 

 

Pool details

24200 gallons

Vinyl

Hayward de filter 3620

Hayward h250 gas heater

Hayward cl2002s chlorinator

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JCMC70 posted this 05 July 2021

Hello,

With all due respect, the water in your pool isn't balanced. Using your test numbers, the CSI (calcium saturation index) of your pool is -1.31. The CSI represents water balance. The closer to 0, the more balanced the water is. Anything below -.30 puts plaster/gunnite pools at risk of etching the plaster. But since you have a vinyl pool, etching isn't a real concern. Anything above +.30 puts the plumbing at risk of scaling. A CH level of 52 is fine in a vinyl pool.

Based on the cya numbers you provided, the minimum free chlorine level for water with 60 ppm of cya should be a minimum of 5 ppm. And that's if the water holds a chlorine level. The target range for proper sanitation in water with 60 ppm of cya is 7-9 ppm. The minimum level for a pool with 80 ppm of cya is 6 ppm minimum and 9-11 ppm for the target range.

The 6 lbs of 70% shock that you put in the pool should have raised the free chlorine level 21 ppm. plus whatever the chlorinator was adding. The chlorine level dropping to 8.68 in a little over 24 hours tells me that you have organics (alge, combined chlorine, bacteria, viruses, ammonia or other organic contaminates) growing and a one time shock of the pool (what you did wasn't a SLAM) isn't gonna clear them.

To SLAM the pool you need to bring the chlorine level to 24 ppm for water with 60 ppm of cya and 31 ppm for chlorine with 80 ppm of cya and keep it there until the pool loses no more than 1 ppm of chlorine in an overnight chlorine loss test.

If you want to perform a SLAM you will need a FAS/DPD chlorine test kit.

Let me know if you have any questions or if you need additional help

J

94tbird posted this 05 July 2021

I appreciate your response over a holiday weekend. You're blowing my mind with CSI. Why is this not something all these pool stores who do free water testing ever tell you about.  

 

So what your saying, and excuse me if I am mistaken, is that the ideal ranges that Leslie's and other stores publish, and the ideal ranges  the Lamott ColorQ tester I have are incorrect?

 

Leslie's calls for ph to be 7.2 to 7.8, Alk to be 80-120ppm, Ch to be 200-400ppm, and cya to be 30-100ppm.  I am well within their ranges there by their tests.  Am I missing something? 

 

I tested the water last night at 8.68ppm of TCL.  I let the filter run all night again and shut the chlorinator off and this morning got a reading of 8.60.  Am I correct that it passed the overnight chlorine loss test? It appears that I held chlorine overnight without any significant drop. 

 

That being said should I continue to add shock to keep the chlorine super high for another few days? 

JCMC70 posted this 05 July 2021

 

I tested the water last night at 8.68ppm of TCL.  I let the filter run all night again and shut the chlorinator off and this morning got a reading of 8.60.  Am I correct that it passed the overnight chlorine loss test? It appears that I held chlorine overnight without any significant drop.

If the water held the chlorine level, the water is clear and the combined chlorine level is .5 ppm or less then you should be able to continue with normal chlorination. But you will need chlorine levels that your cya level dictates. The Chlorine/CYA Chart shows the level that should be maintained:

chartone

* Not Recommended

Ben Powell and Richard Faulk originally developed the chlorine/cya chart and Richard Faulk (Chem Geek) refined it and published the chart around 2007.

You're blowing my mind with CSI. Why is this not something all these pool stores who do free water testing ever tell you about. 

Probably because CSI isn't something you can test for using a reagent drop, test strip or digital meters. CSI is a combination of PH, Total Alkalinity, Calcium Hardness and water temperature. Some test kits, like the Taylor 7 way kit, include a water balance wheel in the kit. There are pool apps out there that will take the numbers from those tests and calculate the CSI for you.

So what your saying, and excuse me if I am mistaken, is that the ideal ranges that Leslie's and other stores publish, and the ideal ranges  the Lamott ColorQ tester I have are incorrect?

I don't know about the Lamont digital tester but in my opinion the ranges developed by most pool stores and pool sites are generalizations to cover all pool types. As an example, a TA range of 80-120 ppm is useful for plaster/gunnite and some fiberglass pools as they are heavily dependent on water balance. In a vinyl liner pool a TA level of 60-80 ppm is all you need because scaling of the pool surfaces is possible, but not etching of the surface because vinyl liners have no calcium for the water to leach.In plaster/gunnite and some fiberglass pools, the minimum ppm of calcium should be 250, not 200. And the total range is 250-650 with the ideal range of 350-550.As for the cya level, I've never had anyone recommend a level above 50 ppm. As you can see from the chlorine/cya chart levels above 60 are not recommended and when the level gets to 90, it is recommended that part of the water be drained and replaced with non stabilized water.

The bottom line is pool companies offer free water testing so they can sell you pool chemicals. It's been a long time since I've taken a water sample to a pool store. But back when I used them I can't remember a time when they didn't tell me I needed $50 to $100 worth of chemicals 

J

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