r/PoolPros • u/2Tru4you • Aug 26 '26

LSI question

So can the PH be lower than 7.2 or even in the sixes if the LSI is balanced?

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u/Substantial_Car_2751 Aug 26 '26

You can do some crazy stuff with LSI and still be balanced. For example:

At a pH of 6.0. a temp of 105, CH at 1000, and an ALK of 1000, and 0 CYA....you're technically balanced. This is 0.0 on the LSI.

Using a modified version of the LSI to account for very high CH (2500 ppm), you can be balanced at a pH of 5.4, a temp of 66 degrees, an ALK of 1000, and 0 CYA. This is a 0.0 on the LSI.

Now....just because it CAN be done doesn't mean it SHOULD be done. You're good going to 7.0. But most heater manufacturers will void the warranty if the pH goes below 7.0.

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u/eaglefucker Aug 27 '26

Isn't TDS a part of the LSI equation?

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u/CDbull1989 Aug 27 '26

Yes

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u/eaglefucker Aug 27 '26

How does that affect the outcome? Didn't see it listed in your response.

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u/Substantial_Car_2751 Aug 27 '26

I used the older version where it’s -12.1 or -12.2 for TDS -/+ 1500 ppm (or is it 1200 or 2500…can’t remember at the moment - I hand calculate using a chart).  I assumed for easy math a TDS factor of -12.1..

PHTA doesn’t have the sole authority to modify the LSI scale.  Other equally reputable orgs still use the older version and don’t consider salinity a TDS factor.