My pH Won't Stabilise

The pool is beautifully clear since we drained and cleaned it a couple of months ago to get rid of calcium deposits that had formed over the last three years since it was built. Because I suspected the problem was down to high pH, I bought a Hanna digital tester to get a more accurate picture of what is going on. After a month of daily testing, I'm finding that the pH increases by about 0.1 per day and that I have to add HCl about every 6 days to keep it in the range 7.2 to 8.0 - 1 litre of acid brings the pH down about 0.8. The pool is only being used lightly at the weekends at the moment.

I don't read of anyone else having to add HCl so frequently so I'm guessing I'm missing something and any advice would be much appreciated!

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Hello and welcome to TFP! :wave: Since your pool is not new, we can rule-out plaster as the reason for your pH climbing. We know spa spillovers and SWGs can in their own ways contribute to pH climbing a little. More importantly right now, what is your TA reading? If your TA is high (i.e. 100 or more), that could be the reason. An elevated TA will not be able to serve as a good buffer for the pH , therefore pH will climb faster. You might check that to see. Let us know how it goes and if you have anymore questions.

Pool School - Lower Total Alkalinity


LifeTime Supporter
TFP Guide
May 14, 2015
Cartersville Ga
There will be others along with more technical knowledge but I can say that just from looking at your signature I see 2 things that contribute to pH rise. Your water fall and your SWG. Both things are known for increasing pH.

There are other things too. Please post a complete set of water parameters and the testkit you used to obtain them.


Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
Bedford, TX

Welcome to TFP... A Great resource for all your pool questions... :wave:

You have a SWG and waterfall, both will cause your pH to increase over time. In my opinion, the keys to controlling pH is to get both pH and TA under control.

In my case, if my TA is about 70, my pH will stay at 7.8 for several weeks without adding acid.

What is your current pH and TA levels? See more here....

Thanks for posting,

Jim R.


TFP Expert
LifeTime Supporter
Jun 7, 2011
Midland TX
Not unusual at all, and I too suspect you have an upper TA, but the SWG, and SWG will add to the quicker increase as mentioned. Let us know, and we can help.
Sorry to have been quiet on this for so long but been away and unable to do anything. Yesterday I delivered a sample of our pool water to a new lab near here who are going to do what they describe as a complete set of tests and advise what steps if any need to be taken. The test is pretty expensive but I thought it worth the outlay once rather than buying a kit which I still can't lay hands on locally at short notice.

I will post the results and advice here as soon as I get it.

Incidentally, the lab asked for a plan and picture of the pool so I dug a couple out and attach them below to give a better idea of our setup. Water comes from the pump & filter as shown by the blue arrows (although there are actually three inlet nozzles at the end marked "C") and very gently via the spa where, due to a mistake in the design of the lip, it curtains down the surface of the mosaics rather than waterfalling as I had originally expected. Nevertheless it's a pleasing effect (and less noisy!).

Simplified Pool Plan.jpg

Pool Deck Pano High Level.jpg


TFP Expert
LifeTime Supporter
Jan 4, 2016
Sydney, NSW, Australia
Nice looking pool! Welcome to TFP :)

Correcting pH weekly is not unusual, especially if the pool gets lots of use. PoolMath makes it pretty easy to do. Anything up to 7.8 is fine, so don't correct pH unless you see 7.9. Just mentioning this because a lot of people believe there's an ideal number lower than that.

You can try for international shipping of a recommended test kit, e.g. this one: Taylor FAS DPD Test Kit Chlorine - SERVICE SIZE K-2006C $139.99

Occasional testing won't provide the information you need for Trouble Free Pool Care (TFPC). Here's a thread I found helpful when I started out: TFPC for Beginners
Got the results of the test back this morning:

My faith in the lab took a dive when I saw the measurement for pH as my readings for both the day of the sample and today are 7.7 so went to see them with my meter and a new sample. For some reason (they suggest where I collected the sample from and the time of day) I got the same reading as them on the original sample but we both agreed that it's 7.7 today at least. Putting aside the pH, they suggest that the most pressing action is to raise the chlorine level and keep it there with CA.

This wasn't the original issue as per my OP - will their suggestions help keep it stable, do you think?



Bronze Supporter
Apr 20, 2016
Riverview, FL
First, get your own test kit. Needajet has posted link to larger and more expensive kit. There is also a smaller (and less expensive kit) you can but, K-2006 (without the "C"). Whichever, you need to get one or the other so you can have reliable readings.

Using the readings you have, FC (Free Chlorine) should be your first area of concern. FC should be in the 4+ range, getting your test kit then to verify the current level is key. Once you have your own test results post them and others can provide more input.
The lab that just did the test will give me another follow up one at no extra cost next month when I have made some adjustments, but I do want to get a kit of my own in due course. Unfortunately, when you can find one, the price of even the K-2006 over here is about US$160 - a full $100 more than in the US so I may have to wait until a friend comes to visit. Does anyone know if these test kits are acceptable in airline checked luggage?


LifeTime Supporter
Jun 6, 2013
You indicated high PH but what the test you have indicates under 6.3????? Something doesn't add up or the test kit you have for ph is not accurate.
The pH is currently 7.7 and I measured it on the day I took the test sample for the lab as the same. I'm using a Hanna testing meter and calibrate it every couple of weeks to be sure it's accurate. Read my post and you'll see that there is some mystery as to why the original sample I gave them showed a very low pH but today we both agree that 7.7 is correct so no sense in worrying more about it at this point. It's in line with my daily readings so I'm satisfied that we are right now.

The lab have promised me a repeat test because of the confusion but getting the FC under control seems like a good idea before we do it again, don't you think?
Last edited:


TFP Expert
LifeTime Supporter
Jan 4, 2016
Sydney, NSW, Australia
PoolMath uses cookies or your login or somethingorother to save your pool details. You'll see your numbers when you return to it.

Yep, get your CYA (aka cyanuric acid, aka stabilizer) to 30 ppm and use chlorinating liquid to get your FC to 3 or 4, and then use your SWG to hold it there. The fact you're at 0 FC is telling you one of two of these things: SWG has not been putting FC in the water; SWG not putting enough FC in the water, or; organic contamination (such as a nascent algae bloom) is consuming the chlorine.

Their recommendation to shock the pool is a good idea. We would take it a step further, but you don't have the right testing equipment to do it. We would do a SLAM because of the zero FC, and perhaps also do an OCLT to find out if free-floating algae is consuming the chlorine. Given that your water looks ok, algae may be just getting started and still not visible to the naked eye. If you can see any green, then the full SLAM is needed, but you need your own FAS-DPD testing for FC to SLAM or do an OCLT.
Pool School - SLAM - Shock Level And Maintain
Pool School - Perform the Overnight FC Loss Test (OCLT)

You'll pay for a test kit with reduced spending on chemicals and pool maintenance, not to mention reduced grief and effort, along with better pool water.

pH 7.7 is fine. A fair number of people find their sweet spot for pH and TA is right around pH of 7.7/7.8 and they're able to leave pH there for long periods.
So far so good, I think. Last weekend I added 2.5kg of CYA with the aim of bringing it from 0 to 70 since my pool gets a lot of direct sun and has both the SWG and a waterfall (of sorts). I increased the output of the SWG to max for a three days also used a single puck of Chlorine that I had left from the original fill and let it hang in the inlet to the skimmer for a couple of days. The OTO Chlorine test now looks at least a 3 and the pH has fallen to a steady 7.2 so I've reduced the SWG setting to 5 (of 8) and will get the lab to do another test in about 10 days as I'm hoping that the pH will edge upwards a little in the meantime. I'll invest in a proper testing kit at the next opportunity.

Many thanks for everyone who kindly gave their time to advise me on this thread. I've got to say this is about the best support forum on any subject that I've ever used!
Just a follow up...

The OTO drop test has been very yellow since I added the CYA (looked like at least 3.0, but hard to tell as I think the scale is faded) and the pH has been steady at 7.7 according to my digital tester. A few days ago I turned the SWG down to 5 thinking that the chlorine was going to get too high. The pool is super clear and looks great but does taste a little salty. Here is the result of the re-test that the original lab did for me for free:

Test Results Report 2.jpg

My questions are:

  • Should I be adding bleach or will turning the SWG up another notch or so be sufficient?
  • Since I have a SWG and a waterfall (albeit small and feeble) should I increase the CYA to get closer to the 60 ppm that I see is recommended here?


TFP Expert
LifeTime Supporter
Jan 4, 2016
Sydney, NSW, Australia
I wouldn't increase CYA without owning a recommended test kit, so my suggestion is no.

Add bleach to get to 4 ppm FC and crank the SWC up and see if you can maintain it.

Do you know the output of your SWC (should be in lbs/day or grams/hour)?