Questions about recommended TA level for pool with a SWG

[GAR1]

The article on Water Balance for SWGs in the Pool School says it is important to have the TA level at 60-80ppm. This recommended range is somewhat lower than the 70-90+ppm shown for pools using bleach and the 80-120ppm range recommended by the SWG manufacturer (Aquarite),the guidelines included in the Taylor testing guide and both pool stores that I use. I am curious about the rationale for this lower recommended range. I did not see one in the Pool Store or the forums. Does the lower range have something to do with the nature of the chlorine generated by the SWG versus other types of chlorine commonly used? What are the relative advantages/disadvantages of maintaining TA in this range versus in the 80-120 range? Are there any disadvantages/negative effects if the TA level is in the 80-120 range? I am all for maintaining the TA in the lower range because I am constantly battling rising pH rising with dry acid, which lowers the TA. Also, when measuring the TA, should I take into account the cyanuric acid correction factor? Thanks.

 

[JVTrain]

The lower TA for SWG pools is because the salt water cell inherently generates a lot of aeration during its operation. Aeration (outgassing of carbon dioxide) is what drives pH upward. At higher TA levels, the faster this outgassing occurs. That's why with an SWG, the TA recommendation is lower. TA level affects the water's ability to buffer pH changes but even at 60 ppm TA, that's enough to prevent pH swings.

I'd recommend switching to muriatic acid rather than dry acids, unless you're uncomfortable handling MA.

As far as CYA correction factor... I have no idea what that is.

 

[chem geek]

You do not need to adjust TA for the CYA amount. That adjustment is only needed for calculating the Calcite Saturation Index and PoolMath will do that for you automatically. The TA in the Recommended Levels is for your measured TA without any such adjustment and assumes the CYA is in the 60-80 ppm recommended range as well.

 

[GAR1]

Thanks for your quick response. It was very helpful. Regarding using muriatic acid, I can be somewhat of a klutz, so I am a little leery about using it. Other than the cost, are there other reasons you recommend it over dry acid? Is it more effective? Regarding the CYA correction factor, the following is from the “Pool & Spa Water Chemistry A Testing and Treatment Guide” that comes with the Taylor K-2006 test kit.

CYANURIC ACID CORRECTION TO TOTAL ALKALINITY
Total alkalinity is a measurement of all forms of alkalinity including the carbonate alkalinity and cyanurate alkalinity present in a sample. Since water balance calculations only use the carbonate alkalinity portion, a correction (which varies with pH) should be applied to correct for the cyanurate portion. Table K (on page 63) lists these correction factors along with a calculation to obtain carbonate alkalinity levels (Note: While Taylor technologies recommends using the correction, some members of the pool/spa community question its value.)

I didn't know whether the TFP community recommended using the correction or recommends just using the test result without the correction. Attached is a copy of Table K from the guide that shows the calculation FYI.

View attachment Table K.pdf

 

[GAR1]

Thanks Chem Geek. That answers my question.

 

[chem geek]

The main downside to dry acid is that it adds sulfates to the water and those can be damaging to concrete and plaster. Since you have a vinyl pool that shouldn't matter so you can use dry acid if you prefer. It may be more expensive, but probably not too much.