My pH keeps going back up?

Dallas Swimmer

New member
Sep 12, 2020
I went to Leslie's about a month ago & the guy told me that I needed about a half-gallon of acid in my 18,000 gallon SWG pool, so I added acid... about 40% of a gallon.

I had my water tested at Leslie's several days later, and it barely budged... from 8.4(?) to 8.3 (on 8/30.)

The 8/30 readings from Leslie's are as follows:

3483 ppm salt (high, but the other pool store said I was at 2600 & my pools control panel reads 3000)
3.27 ppm free Cl
0.5 ppm combined Cl
8.3 pH
106 ppm TA
143 ppm Ca Hardness
36 ppm CYA

He recommended 20-25 lbs of Calcium hardness, but he didn't have a significant quantity in until maybe the next truck.

Not realizing that my pH had barely budged, I figured in the meantime, I'd throw some chlorine shock at it & bought two bags of their really concentrated stuff, which I put in that night.

I got impatient about the idea of waiting for Ca Hardness, so I ended up going to another pool store the next day.

The other pool store gave me these test results the next day, on 8/31:

2600 ppm salt (massively different reading)
10 ppm free Cl (expected it to be high -- just shocked the pool)
10 ppm total Cl
8.2 pH
88 ppm TA
200 ppm Ca Hardness (somehow it magically went up?)
40 ppm CYA

Even the 8/31 test had me rather low on Ca Hardness, so I proceeded with adding 10 lbs of Ca Hardness.

It rained several days ago, and the pool's walls started to turn a bit green again.

Seeing as how the two different pool stores have me substantially different readings (3483 vs 2600 ppm salt, 143 vs 200 Ca Hardness, 106 vs 88 TA) and after realizing that my pH had barely budged even after adding quite a bit of acid, I wasn't sure if I should be skeptical of their test results or if adding the shock threw the readings off, so I ordered a Taylor K2006 off of Amazon so I could test my water much more often & know that I wasn't being played games with.

The K2006 came in on 9/10 & I tested the water yesterday, 9/11.

6.6 ppm free Cl
0.6 ppm combined Cl
8.2 pH
90 ppm TA
250 ppm Ca Hardness
20 ppm CYA (a little low, but I do have quite a bit of FC anyways)

(Note: I also added phosphate remover about a month ago [from 1500 ppb to 0], 10 lbs of calcium hardness on 9/1 [150-200 ppm to 250 ppm (as measured by new K2006)], and 2 lbs of chlorine shock on 8/30. All of these treatments were from quite a while ago, so they seem largely irrelevant & I should just go by what my K2006 tells me, right?)

I did the acid demand test as well, and the table said to add 1.72 qts, so I went ahead and added about that much in.

I tested the pH about two hours later, and it was 7.5, but I figured I'd add even more acid in, just to try to get rid of some of the new algae growth and I've already had trouble keeping the pH down, so why not? (I didn't test the pH again after adding the extra cup of acid, but I figured it should've put me around 7.4.)

I've added NOTHING in the past week or so except for this roughly half-gallon of acid yesterday.

Well today I go out there, about 22 hours later, and the pool is looking a bit better, but it's not perfect.

With that pH drop, we're on the right track though, so everything seems good, right?

Out of simple curiosity, I tested the pH again, believing that it'd be around 7.4.

I'm not at 7.4. I'm back up to 7.9.

Why is it that I've added nearly a gallon of 30-35% acid into my 18,000 gallon pool now, and I'm back up to 7.9 pH? Should I just keep adding acid until it stays down?

The pool was re-plastered a few years ago & the plaster seems to be damaged. Why is this the case, when my TA & Ca Hardness were relatively fine & my pH was through the roof? If anything, with the exceptionally high pH we've had in the past, we should have scale build-up, not plaster damage!

(Pictured: initial ~8.2 pH test from 9/11, and the ~7.9 test from today; I didn't take a picture of the 7.5 pH test from yesterday because I thought my pH troubles were finally gone.)


Last edited:


Well-known member
Aug 31, 2019
Phoenix, AZ
I'm a beginner so we might want to get some confirmation from others before you do anything but here are my thoughts:

No one on this forum is going to take pool store tests seriously, just FYI; so it's best to throw those results out and start with some "good" data.

Also, you mention you want to get the pH correct to get rid of the algae, however I don't think pH has much effect on algae growth. It might effect it a little, but the main thing you want to make sure is your FC not dropping below the recommended amount. Also, if you have an algae bloom, you need to SLAM, or you'll just continue fighting the algae without winning.

Why is your pH rising so quickly, here are a few possible reasons
* You aren't measuring correctly? The pH test is odd in that you have to have good sun light, have to have the correct background, etc. Just verify you are holding it far enough away, with a white background, etc.
* Same with TA, are you measuring correctly? I know the TA test in the tf100 kit has an issue where you need to wipe the dropper, make sure you aren't running into that issue? The higher your TA, the quicker your pH will rise.
* I don't think tests above 8.0 pH are reliable? It's possible your pH was higher than 8-8.5 before, but you didn't know it and you've just been bringing it down more than you think?
* These are all just thoughts off the top of my head. It does seem weird for your pH to go from ~7.3 to 7.9 in less than 24 hours.

My recommendation for pH would be:
verify you are performing the tests correctly. Test FC, TA, and pH at the same time for a couple days, record the results. Then you can get a better understanding of what your pH is doing day after day. Also, meassure the TA, and pH of your fill water, post those results.

My recommendation for your algae issue:
Do an OCLT and report back with the results. If you fail the OCLT, SLAM the pool, but make sure your pH is between 7.2-7.5, since you can't measure the pH when the FC level is at SLAM level.

Good luck!


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

I'd just as soon let it dribble down my leg rather than walk into a Leslies to just use their bathroom.. :mrgreen:

pH and algae have nothing to do with one another..

pH going up is kind of natural.. Things that make it worse are aeration, caused by constantly running a water features, new plaster, and high TA..

If you have algae, then you have to SLAM your pool.. SLAM Process

Raising your FC to normal TFP levels may make the pool look better for a time, but if all the algae is not dead, it will just come back.. The SLAM is the only answer.


Jim R.
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Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
Franklin, NC
As @Cwiggs indicated, I'm ignoring everything above the statement - " The K2006 came in on 9/10 & I tested the water yesterday, 9/11. " it's all junk, stop going to the pool store. They just want to sell you stuff like that phosphate remover.

First, you comment " I've added NOTHING in the past week or so except for this roughly half-gallon of acid yesterday. " scars me. Chlorine is a consumable item and needs to be added daily. No/low chlorine = green pool. You may not see it, but algae will be growing.

Next, pH - it always rises (OK, almost always). In most pools you will add it once or twice a week. Again, it's a consumable item.

You have seen green, so it's time to SLAM the pool. You have the the kit.

Please edit your signature and add the following information so we can better frame our answers to you. You keep talking about CH, but you may not need it.

  • List what test kit you use to test your water
  • The size of your pool in gallons
  • If your pool is an AG (above ground) or IG (in ground)
  • If it's IG, tell us if it's vinyl, plaster/pebble, or fiberglass
  • The type filter you have (sand, DE, cartridge)
  • If you know, tell us the make and model of your pump and filter.
  • List any other equipment you have: SWG, second pump, etc.
  • Please mention if you fill the pool from a well or are currently on water restrictions
  • mention if you fill the pool from a well or are currently on water restrictions
  • Information in your signature will show up each time you post and it makes advice more accurate as we know what equipment we are dealing with.

How much Pool School have you read? Start with these:

So again, welcome to TFP!
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Gold Supporter
TFP Guide
Nov 12, 2017
Central California
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Hey Dallas, you're getting some great advice here. Just follow it and you'll be good-to-go. Especially the part about the dribbling! :LOL:

I'll only add: you cannot measure ph 8.2 with the K-2006. You can sort of interpolate between 7.6 and 7.8, like that. But anything "purpleier" than 8.0 means you don't know what the pH is (just that it's higher than 8.0). When that happens, you "pretend" you've got 8.0 for the purpose of dosing. Say you want to get to pH 7.6. You'd do your dosing calculations based on 8, dose that amount, then retest in an hour or so (pump running, of course). If you get 7.6, you're done. If it's still above 8, you go again, same scheme. If it's between 7.7 and 8.0, then you know where you really are and then you dose one more time to get to 7.6.

And as pointed out, you defend and destroy algae with FC, not pH (chlorine, not acid). Read your homework assignment and it'll start to come into focus. Many of us had to read it a few times, before it sunk in. So no worries if it's not all crystal clear after the first read.

Welcome to TFP!


Bronze Supporter
Jun 1, 2018
Hernando, Ms
@Dallas Swimmer
Glad u got a good test kit & are ready to take control of your pool😊

I just read through the thread & I know u have alot of info to go through as everyone pretty much covered all the bases but the jest of it is -
*1) lower ph to 7.2 & SLAM w/ liquid chlorine. ASAP to eradicate your algae problem. Use PoolMath to calculate additions- it also has a helpful log👍🏻

*2) AFTER you complete the slam
(all 3 end of slam criteria met)
You should then increase your cya to 60/70 so the chlorine your swg produces lasts in the hot Texas sun.
I imagine that’s what got u into algae territory in the 1st place.
The chlorine from the swg is produced slowly over time & needs that cya buffer to protect it from the sun.

A swg is only meant to maintain 2-4ppm/daily fc loss not overcome an algae/organic issue.