When Alkalinity is to low ?


Aug 13, 2020
Hi Guys,

When ALK is to low ... I know we aim for 50, but even at 50 my pH goes up over 8 after one use.

Is 40 safe for Acrylic spa.

Thank you

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
A TA of 50 is about as low as you want to go. A TA of 40 isn't going to hurt the tub itself, but once yo're below 50 the pH can become unstable and, ironically enough, drop unexpectedly on you. Have you considered borates? It's talked about a bit in the link below.



Bronze Supporter
Oct 20, 2017
South-Central WI
Just to verify, the proper way to do the TA test is to test until the last drop added does not cause any further color change, then subtract the last drop. In my case, when I'm approaching the end of the TA test I usually see the green fading away with maybe a tinge of red on a drop, no green with light red on the next drop, then a bright red on the following drop. Another drop after this does not further change the color, and so I do not count it. When I first started testing I didn't realize this was the case, and stopped when I first saw the barest hint of red, leading to me thinking the TA was 10-20 ppm less than it actually was. I thought it was 50, when it actually was 60 or 70. This lead me to have the same questions you did.

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