PH and Alkalinity

[Patrickoleary]

I’ve read a ton of threads here and I’m experiencing something I didn’t expect.

Converted to a SWCG pool recently. Love it from a CL standpoint. I’m just having issues with PH and alkalinity.

20k gallon, vinyl.
PH 7.7
Alkalinity 54

The PH rose from previous of 7.4 across 2 weeks. To be expected in salt pool. Per everyone advice in many threads, adjust alkalinity first. I add baking soda. Then test.

PH 7.7
Alkalinity 85

Ok. So then I want to add some 31.5% Muriatic Acid to get PH 7.4. Use the pool app to calc. Add 2 cups muriatic acid.

PH 7.4
Alkalinity 54

The thought was that adjust alkalinity first, then PH and the Alkalinity won’t move as much as the PH. But that’s not the case. The Alkalinity moved a ton. Thoughts?

 

[ajw22]

Welcome to TFP.

What test kit are you using?

Any pH in the 7s is okay. Don’t lower pH until it gets to 8. Then lower it to 7.6.

TA of 50 or above is ok. If your pH is in the 7s and rising then your TA is ok.

I suspect your TA testing is not reliable or accurate.

 

[Tpopz]

The only time I shoot for a TA target is after a water change in my hot tub. With the constant upward pressure on pH from aeration and use of borates, I like my TA around 60 within a day or 2 of changing water.

In my pool(vinyl, no fountains or waterfalls), I simply manage pH.....the TA takes care of itself.

 

[Patrickoleary]

LaMotte digital. So, the test should be reliable.

 

[Patrickoleary]

It feels like the general theme here may be that I’m messing with it too much. I’m a first year pool owner. Probably testing every 3 Days or so.

I’ve just been following the app. The TA says 60 to 80 range.

 

[ajw22]

All chemicals are not equally important in your water.

CL and pH are primary for good water health.

CYA is secondary and determines your FC level.

TA and CH are not important alone but affect other things. In general TA level only needs to be adjusted when there are issues with pH. The main reason you regularly test TA is it affects the calculation for how much acid is required to change the pH.

 

[Patrickoleary]

All chemicals are not equally important in your water.

CL and pH are primary for good water health.

CYA is secondary and determines your FC level.

TA and CH are not important alone but affect other things. In general TA level only needs to be adjusted when there are issues with pH. The main reason you regularly test TA is it affects the calculation for how much acid is required to change the pH.

Thanks. I’ve been following the app and read a ton of articles. What I’m seeing is that I shouldn’t worry so much about getting every number dead nuts perfect. Instead focus on CL and PH.

Though...With a SWCG pool, I see conflicting info everywhere on CYA. Most articles say (including this site) you must keep at 70-80, but then don’t explain why. Only that for Salt it is required. The Hayward manual for the 940 generators I installed says 30-50, but that goes against everything I read on the site about CYA. Seems to me that CYA for fresh and salt should be similar, unless there are properties with the salt that inhibit algae growth, thus you can keep your CYA higher and let your chlorine last longer.

 

[Tpopz]

I see what you’re saying about the CYA, SWG levels. My take is SWG allows you to keep a higher CYA level to combat UV losses because it’s a steady supply, not that it requires a higher CYA level. When you are dosing with liquid chlorine, a lower CYA allows you a greater range of effective FC because FC will be highest at dosing time and continue to diminish.

 

[ajw22]

Though...With a SWCG pool, I see conflicting info everywhere on CYA. Most articles say (including this site) you must keep at 70-80, but then don’t explain why. Only that for Salt it is required. The Hayward manual for the 940 generators I installed says 30-50, but that goes against everything I read on the site about CYA. Seems to me that CYA for fresh and salt should be similar, unless there are properties with the salt that inhibit algae growth, thus you can keep your CYA higher and let your chlorine last longer.

TFP guidelines are based on more modern chemistry findings than the manufacturers.

Read the section on CYA in

Pool Water Chemistry

This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...

www.troublefreepool.com

Salt Water chlorine Generation (SWG) pools seem to require a higher level of CYA, about 70-80 ppm, to operate efficiently. The theory is that the CYA is slow to "store" the chlorine as it is being generated so without enough CYA there is a build-up of chlorine that degrades the performance of the salt cell. I would prefer that the SWG manufacturers offer a larger lower-power (per length) cell that would work efficiently at lower CYA concentrations.

 

[Patrickoleary]

TFP guidelines are based on more modern chemistry findings than the manufacturers.

Read the section on CYA in

Pool Water Chemistry

This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...

www.troublefreepool.com

Salt Water chlorine Generation (SWG) pools seem to require a higher level of CYA, about 70-80 ppm, to operate efficiently. The theory is that the CYA is slow to "store" the chlorine as it is being generated so without enough CYA there is a build-up of chlorine that degrades the performance of the salt cell. I would prefer that the SWG manufacturers offer a larger lower-power (per length) cell that would work efficiently at lower CYA concentrations.

GREAT info. Thanks.

 

[Clive64]

LaMotte digital. So, the test should be reliable.

I have the same test kit, I think (ColorQ Pro7) but I have done some tests, which show that the results are not as reliable as you might expect. The size of the 5 drops can affect the result significantly (do you put them in holding the bottle horizontal or vertical?), and if you accidentally put in an extra drop, you get a very different result. Also, if you re-test 5 or 10 minutes after the first test, using the same coloured test tubes (i.e. just go through the menu of tests and put the same tubes in that you used before (you can’t re-do FC, of course) then you also get a different result. This raises the issue of should you wait for a few minutes after adding the chemicals before testing the tubes, or is the most accurate reading immediately after adding the chemicals? For CYA, waiting EXACTLY 2 minutes makes a difference. Earlier or later and you get a different result. Try doing three tests on the same water, immediately after each other (i.e. go through the whole test procedure three times, adding the chemicals) and compare results. The variations will surprise you, and indicate the margin of error that you can get, which will put the measurements into perspective.