How high can Ph rise if it just left to rise with not adding acid?


Well-known member
Jun 15, 2019
Houston Texas
My good friend lives around the corner and we had our pools built last year by same builder at the same time.

I found this great site and do all the testing/water chemistry on my pool.

He has a "pool guy".

Out of curiosity, he brought over his water for me to test yesterday.

I use the Taylor 2006 testing kit.

When i did the Ph test, the color immediately was a very bright purple....obviously well above the top reading of 8 on the comparator tube.

So my question is, if you never put in acid to bring PH down, how high can it go?

Another interesting test result was his chlorine which was basically 0...maybe 0.5. His CYA was 90. He finally listened to me last month and drained about 6 inches of water. (told him to keep draining)

I asked him why his chlorine was so low. He said his pool guy likes to run it that way in the winter. I can only guess that the pool guy knows the trichlor pucks are very acidic and a low PH combined with low water temp, makes a very negative number on the CSI.

He said it's been this way all basically 0 FC with 90+ CYA and no algae all winter

Does the low water temp help that much to prevent algae growth?

Hmmmm....puzzling to me...trying to understand

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Does the low water temp help that much to prevent algae growth?
Not always totally, but it helps slow it down quite a bit. My water temp is approaching 70, so my pool maintenance vacation is about over.

As for the pH rise, I suspect it depends on factors such as the age of the plaster, TA, water temp, amount of aeration, etc. Some may level-out at about 8.2-8.5, while others can easily go over 9 or more. Maybe @JamesW or @JoyfulNoise have some pH examples to share.


Well-known member
Jun 15, 2019
Houston Texas
Hey there Texas Splash!

I suspect his water has to be close to 9 with that color I saw...was shocking to see.

Yes my pool maint vacation is almost over too!

Live south of Houston in League City. Going to put out my weed n feed for the yard tomorrow and maybe take a stab at cleaning my pool filters for the first time...might need a few beers as I suspect it will take some time (cartridge filters)

I've tried this winter to keep my FC at 5 or higher as my CYA is now avoid any algae ...but was thinking, could save a little $ if I could let the FC drift a bit lower...I dont know though...just doesn't seem worth the risk...pool was built last June and never had algae...would love to keep it that way!

Take care my friend!


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Your friends pool will likely develop scale problems eventually which his pool guy will be happy to take care of for an additional charge. See how it works? No incentive for a pool guy to do it right.


TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
Water with an appreciable carbonate alkalinity if left on its own can easily see the pH rise to 8.5. It will usually top out around the mid-8’s. However, your neighbors pool water may have had stuff added to it that would cause excessive pH swings. Many pool service companies will use solid chlorine which can drop the TA and pH over time. Then, to restore pH, they’ll throw in a large amount of soda ash (sodium carbonate) which can cause the pH to jump up very high.

As for algae growth and temperature, most species of algae found in pool water will have almost zero growth rate once the temperature goes below 60F. There are species of algae that can grow in near-freezing water temperatures but they are not typically found in pools. This is why TFP always recommends waiting to open or close a pool until the water is around 60F.
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