Chlorine level "stuck"

[jfe]

Hello - I keep my pool open all year round so we can enjoy the spa. I am currently using a tab chlorinator as my primary and also have ozone. I am in mid GA, so the weather has been relatively mild. I have noticed that my CL level is still relatively high so I took the tabs out of the chlorinator a week ago and the level is still high. My test results as of today are:

FCL - 5.5
TC - 5.8
ph - 7.5
ALK - 76 (I know I need to raise this)
TH = 250
CYA = 98

I have not used the spa yet this winter so I have been slack on testing the water. Can anyone give me some insight as to why the chlorine seems to be "locked" and won't dissipate.

Thanks
45000 IG unite pool, Jandy DE filter, Jandy LRZ heater, Polaris 280, 1.5 hp Jandy pump

 

[poolsupplysales]

It takes longer for the chlorine to burn off in the winter due to the lack of uv rays of the sun and less swimmers.

 

[RobbieH]

Colder weather and less daylight time means less chlorine usage.

By the way, your CYA is way too high, and is due to using those trichlor tabs.

TA of 76 is just fine.

 

[jblizzle]

+1 to what RobbieH said

Although that TA is fine for SWG or people who use liquid chlorine, people who use tablets must continue to raise the TA due to the use of acidic tablets. But, using the tablets also obviously results in the CYA getting too high.

Recommendation would be to replace half your water to get the CYA in range and then switch away from the tablets.

 

[jfe]

Thanks for the tips. I have started researching my alternatives to the tri-chlor tabs. I am leary of SWG becasue of all of the natural stone I have around my pool. My concearn with liquid is that I would need a fairly large tank due to the volume of the pool.

 

[Stuamurr]

For chlorine to be wholly effective with a CYA level of 98 you should be shooting for a FC residual of 7-12ppm, so actually your chlorine level is too low at the moment.

You should consider diluting your pool water to bring the CYA level down, replacing 50% of your water will reduce your CYA by 50%, so down to a more acceptable 49ppm CYA, which will realise a more preferential 4-6ppm FC Requirement.

Cessation of the use of Tri-Chlor pucks should be high on your priorities, by switching the liquid bleach/Sodium Hypochlorite or Calcium Hypochlorite.

Given that you have listed Total Hardness instead of Calcium Hardness are you merely using test strips to test your swimming pool? As these can be wildly inaccurate I would highly recommend the purchase of a more accurate and robust test kit.

Total Alkalinity is fine where it is, read the following pool school articles for further information:

pool-school/chlorine_cya_chart_shock
pool-school/recommended_levels

Regards
Stuart

 

[jblizzle]

True that is a larger pool. You would likely need 200-300 oz of 6% bleach every day after you get the CYA in check.

Stuart does raise a good point ... how did you get the test results?

 

[jfe]

Thanks - I mis-stated TH for CH. I am using the Taylor K-2006.

With regards to the liquid bleach, is my assumption correct that I would need to have a large bulk tank to feed my 45k + gallong pool?

 

[chem geek]

If your pool (in the summer) had a usual 2 ppm FC per day chlorine usage, then that would take 90 ounces (almost 3/4 gallons) of 12.5% chlorinating liquid per day. With an automatic feed system such as The Liquidator, it can hold 8 gallons so would need refilling at least every week. With a peristaltic pump, you could get a larger container and purchase larger carboys (15 gallons) at a time.

If you have summer or winter rains, you should use them to overflow the water to help dilute it over time. You might be able to supplement the chlorinating liquid with some Trichlor which will help with the volume of chlorine you need to add. The 2 ppm FC per day would be 13 ounces of Trichlor or a little more than 1-1/2 3" (8-ounce) pucks per day or close to 2 3" (7-ounce) pucks per day. However, if there were no water dilution, then using only Trichlor at 2 ppm FC per day would raise the CYA by 36 ppm per month.

Note that if the ozonator were powerful enough to have a significant effect oxidizing substances in the pool, then it would increase chlorine demand as well since ozone reacts with chlorine. You might see as a test if the chlorine demand drops if you turn off the ozonator. If it does, then you could consider not using it.

 

[jfe]

That is a good idea. I may look at adding liquid next year and using the tri-chlor on an as needed basis. Is it ok to shock the pool in winter, understanding that it will take longer for the level to drop due to the temeprature and sunlight.

Thanks for you help

 

[jblizzle]

Why do you feel the need to shock? Also, do you understand what we mean by the Shocking Your Pool process?

There is no problem following the process in the winter.

 

[RobbieH]

Chem Geek is dead on. Note the size of my pool. When I had a Liquidator, I refilled once per week. Unfortunately for me, I travel a lot and a week of chlorine was not enough to keep mine properly treated for the amount of time I was gone. It may work fine for you. You do have to purchase a lot of bleach, keep in mind that's 8 gallons a week! That's just over 6 big bottles of bleach. I was buying them 8 cases at a time (3 bottles each) at Costco, and storing them until needed. I don't have stone around my pool, and for me the SWG was the logical choice.

It is easier to shock in the winter because you lose less chlorine to the sun. You will certainly want to shock based on the instructions in pool school, do not add powders to your pool to shock.

Just don't forget, even on a temporary basis, trichlor tabs will drive up your CYA.

 

[UnderWaterVanya]

Thanks - I mis-stated TH for CH. I am using the Taylor K-2006.

For all of the tests? I ask because the numbers you are giving us don't make sense to me based on the accuracy range of the 2006 kit.

FCL - 5.5
TC - 5.8

What test in the K-2006 did you use for FCL and TC? There are two that might be used, one is the FAS-DPD test which uses a powder and then drops and goes through a color change. That test typically gives results in 0.5 or 0.2ppm. The 0.2ppm is for the 25ml sample, the 0.5ppm accuracy for the 10ml sample. Did you perhaps misread the numbers or type them wrong here? If not I'm stumped as to how you got 5.5ppm for the TCL. Another option is a DPD color matching test; but I don't remember if the K-2006 comes with that or the OTO Chlorine test (OTO has a yellow color match scale vs. pink for the DPD test)? Even if you did use the DPD test I am almost positive that test tops out at 5ppm unless you mistakenly read from the bromine scale not the chlorine scale.

ALK - 76 (I know I need to raise this)

How did your test give you an Alkalinity of 76? The test measures in 10ppm or 25ppm increments normally.

CYA = 98

How did you measure a 98 CYA? Was it close to 100 but not quite there? If so you should probably recheck with 50% tap water and 50% pool water and see what the result is - sometimes the test will read near 100 and actually be over it by a good margin. Since the test tops out at 100 it's helpful to perform the test at 50/50 dilution (1 part pool water to 1 part tap water) when the result is near 100 to get a more accurate picture. The result from the 50/50 test is doubled to give the actual CYA level - this will help you know where you stand and not have you do a 50% water change only to find out that wasn't enough.

 

[chem geek]

Is it ok to shock the pool in winter, understanding that it will take longer for the level to drop due to the temeprature and sunlight.

If you are keeping the pool open (i.e. circulation pump running) during the winter, then you don't "shock" the pool but rather just maintain the chlorine level as usual. It just takes less frequent chlorine addition to do so because as the water temperature drops and there is less sunlight, the chlorine demand drops as well.

 

[jfe]

I actually have two different test kits. I use the Lamotte 2056 and then the Taylor to check. The numbers I gave are from the Lamotte - and then I checked the AKY, hardness and CYA with the Taylor. I did not run the CL with the Taylor because the Lamotte seems to always be accurate with regards to CL

 

[UnderWaterVanya]

Re: Chlorine level "stuck"

I actually have two different test kits. I use the Lamotte 2056 and then the Taylor to check. The numbers I gave are from the Lamotte - and then I checked the AKY, hardness and CYA with the Taylor. I did not run the CL with the Taylor because the Lamotte seems to always be accurate with regards to CL

Got it. On the CYA you may want to try the 50/50 dilution - accuracy drops but it can show > 100 which the undiluted Taylor test can't.

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