Boric Acid Measurement in Pool Math?

[PoolSleuth]

I just added 50 lb of boric acid to my 26,000 gal in ground pool. I understand that with boric acid added, the chlorine demand is 5% of CYA vs 7.5% of CYA without boric acid added. Is there a way for the pool math app to expect/demand less chlorine after boric acid is added, taking that into account for the CSI calculation?

 

[mknauss]

There is no change to the FC target due to using borates.

 

[JoyfulNoise]

You are confusing adding borates with using a salt-water chlorine generator (SWG). When you chlorinate your pool manually with liquid chlorine, the correct FC/CYA ratio is 7.5%.

 

[PoolSleuth]

You are confusing adding borates with using a salt-water chlorine generator (SWG). When you chlorinate your pool manually with liquid chlorine, the correct FC/CYA ratio is 7.5%.

Oh, so given that and the fact that I don’t use a SWG and I use 73% cal hypo, what % of my CYA is my chlorine demand?

 

[Newdude]

what % of my CYA is my chlorine demand?

It changes throughout the season with less at the ends and more in the middle. You need to adjust your daily dose so that after the daily loss, you are still free and clear above min at the next test/dose time.

The UV demand more or less follows a pattern besides an occasional curveball due to a particularly hot/cool spell.




3 ppm may be a week-long dose in April, or a 3 hour dose at lunchtime in August. The chart doesn't take that into account and if you need to go over target to achieve the mission, then so be it.



Most of us treat low target as our min, and the difference to absolute minimum is our safety net. The closer you land to min, the closer you need to pay attention so you don't fall too far.

 

[JoyfulNoise]

Using cal hypo is also considered “manual chlorination” like using liquid chlorine. You should follow all recommendations that pertain to liquid chlorine.

Please note that TFP doesn’t recommend using cal hypo regularly. It typically raises pH a lot and can cause temporary cloudiness. If you ever have to perform a SLAM on your pool, you must liquid chlorine for that.

 

[PoolSleuth]

If you ever have to perform a SLAM on your pool, you must liquid chlorine for that.

Thank you for these insights. Can you help me understand why liquid chlorine must be used for a SLAM? Does the cal hypo raise the pH so much as to render the chlorine ineffective?

 

[JoyfulNoise]

When performing a SLAM it is necessary to add enough FC to reach and maintain a level that is 40% of the CYA value. That is typically a very large amount which, if one were to use cal-hypo, the water would cloud up significantly. There is also the issue of pH since one can not measure pH during a SLAM due to high FC. Liquid chlorine is only slightly alkaline on net balance of reactions and so the pH will not change much during a SLAM.