The Low pH Danger Zone: Bob Lowry Breaks It Down

Ever wonder why a pool can look fine one week and show stains, rough plaster, or a failing heater the next? The culprit is often low pH—water that turns aggressive, dissolves metals, and etches surfaces long before the damage is obvious. We walk through how acidic water behaves, where metals come from, and why stains show up only after the water hits its saturation point.

We dig into real-world service scenarios: vinyl and fiberglass pools that trend acidic because they lack buffering minerals, spa tubs that swing wildly depending on chlorine type and use, and the risky combo of low pH with cheap test kits that feed bad decisions. You’ll hear why investing in a reliable photometer that reads copper and iron saves you from surprise stains and equipment corrosion, plus a clear plan for when to use soda ash, borax, or baking soda. We also share a fast spa recovery routine: raise alkalinity first, then aerate to lift pH without overshooting.

Along the way, we challenge old chlorine wisdom. With cyanuric acid in play, the classic HOCl charts don’t tell the whole story. The smarter approach is keeping free chlorine appropriate to CYA while holding pH near 7.5 for swimmer comfort and stable balance. We cover borates as a pH buffer, how they affect alkalinity readings and the saturation index, and why soda ash lifts pH and alkalinity more strongly than bicarb when both are low.

• why low pH makes water aggressive
• etched plaster, corroded components, invisible metals
• saturation points leading to staining
• value of accurate copper and iron testing
• vinyl and fiberglass pH drift and tablet use
• spa chemistry, aeration, and quick rebalancing
• comfort thresholds for bathers around pH 7.5
• choosing borax, soda ash, or bicarb by goal
• borates’ impact on readings and stability
• chlorine effectiveness with cyanuric acid
• practical dosing plans and test habits

Are you a pool service pro looking to take your business to the next level? Join the pool guy coaching program. Get expert advice, business tips, e

Support the Pool Guy Podcast Show Sponsors! 

HASA 
https://bit.ly/HASA

The Bottom Feeder. Save $100 with Code: DVB100
https://store.thebottomfeeder.com/

Try Skimmer FREE for 30 days:
https://getskimmer.com/poolguy 

Get UPA Liability Insurance $64 a month! https://forms.gle/F9YoTWNQ8WnvT4QBA

Pool Guy Coaching: https://bit.ly/40wFE6y

Chapters

• 2:39 Welcome And Coaching Invite
• 3:25 Why Low pH Is Dangerous
• 6:03 Metals, Saturation, And Staining
• 7:33 Invest In Accurate Water Testing
• 9:58 Vinyl And Fiberglass pH Drift
• 13:03 Spas, Chlorine Sources, And pH Swings
• 16:04 Comfort Range And Irritation Thresholds
• 18:04 Raising pH: Borax, Soda Ash, Bicarb

Transcript

SPEAKER_00: 1:51

Hey, welcome to the Pool Vay Podcast Show. It is Bester Bob Lowry. I'm going to talk to Bob Lowry about low pH and the dangers of having really low pH in your pool. And of course, Bob Lowry was the premier chemical expert in the pool industry, and he has a wealth of knowledge to share with listeners, even after, of course, his passing a few years ago. These recordings I think are a great asset to the pool industry. Are you a pool service pro looking to take your business to the next level? Join the pool guy coaching program. Get expert advice, business tips, exclusive content, and get direct support from me. I'm a 35-year veteran in the industry. Whether you're starting out or scaling up, I've got the tools to help you succeed. Learn more at swimming poollearning.com. Let's talk about something that we don't hear much about, but recently I had a member of my group, he had a vinyl pool that had a pH of six, which probably would be lower than that in a lot of cases, depending on the test kitty was using. And low pH typically is not a problem you hear about. High pH is something that we hear about a lot more, but low pH can be a big problem also. What happens if the pH gets too low in a pool for a long period of time?

SPEAKER_01: 3:08

Well, when the pH is low, um the water gets to be what we say is corrosive or aggressive. And it can in a in a plaster pool, it can dissolve or start to etch the plaster. And so you get the plaster instead of being real nice and smooth, becomes kind of rough. So we get etched plaster, we get corrosion of equipment. So the metallic parts that are in the any of the components in the system, whether it's the heater header or the impeller on the pump or whatever, whatever is in metal in the pool can start to dissolve also. And then the dissolved metal gets into the water and it is invisible until it gets to a certain level. And that certain level is what we call the saturation point. When it reaches the saturation point for those conditions, then the water can't hold anymore, even though more is dissolving. When it does that, then it starts to precipitate the metals and we start getting staining. Usually, when we get staining, it's because we've dissolved some of the metal components in the pool. The other reason, of course, is if you're getting metal in the incoming water. And copper and iron are both allowed to be in drinking water. They're allowed to be at a low level. So when you add water to the pool, when it dilutes and everything, you know, it's not such a big problem. But eventually you can build metals up to the point where they can stain the pool. So it is something that once in a while, as a service tech, uh maybe every couple of months, you should run a test for iron and copper and see if the level's gone up.

SPEAKER_00: 4:58

And I don't want to plug too many products, but I have the new color Q Pro 9 2X or 2X Pro 9. And I really like the fact that that photometer tests for copper and iron. I think if you're a pool professional, you should have some way of testing for copper and iron in the water as part of your regiment.

SPEAKER_01: 5:16

Absolutely. You you know, I and I often tell guys, listen, you know, you're gonna tell me you don't want to spend six or seven hundred dollars on a test system, but you just spend$40,000 or$50,000 on the truck that you drive around in to take care of the pools, you know, and and how do you justify that when you can't spend$500 on a test custom test system? So uh get a good test system. You test the water every time you go to every pool. If you're getting bad results and adding chemicals based on those bad results, are isn't that test kit affecting your life, your livelihood, your reputation, and and you're letting it fall on a on a cheap piece of junk test kit? You know, get a good one, get some good answers so you can add the right chemicals to the pool and do your job right.

SPEAKER_00: 6:09

Yeah, exactly. And so back to the low pH here on a vinyl and fiberglass pool, why is it that the pH seems to always drift lower on those surface types? And I know that a lot of fiberglass manufacturers will avoid the warranty on you if you use tablets, three-inch triclare tablets, because I think because those lower the pH, of course. And so why with that pool surface type are we all running into lower pH?

SPEAKER_01: 6:34

The vinyl, I guess we should back up. On a plaster pool, we've got some alkalinity and some calcium coming out of the pool itself and dissolving into the water. It's just a little bit, but it's enough to be uh to keep the water in balance. But what happens is with a vinyl pool, there isn't any source. And so once the pH and alkalinity get a little bit low, the water becomes aggressive and it's looking for something to dissolve. And if there's any metal that starts dissolving it, if if if um interestingly enough, low pH actually affects the vinyl more than chlorine level does. When I was at when I was at Leslie's as their technical director, one of the things I did was I took pieces of vinyl and I literally poured liquid chlorine on top of vinyl fresh out of the jug onto the vinyl and it didn't do anything. On the other piece of vinyl, I put one drop of murianic acid and the color disappeared out of the vinyl. One drop and it disappeared to the color. It made a it made a white spot on blue vinyl where where one drop hit it. So um low pH is no good for vinyl. But it goes low because there's not a source of alkalinity and calcium that's coming out of the walls.

SPEAKER_00: 8:08

Is that true also for hot tubs? The above-ground fiberglass hot tubs. I'm always running into those with low pH also. Or is that the bather load? What can be causing that in like a 350-gallon above-ground hot tub?

SPEAKER_01: 8:24

Well, that can be uh that can be the chlorine source. If you if it's a busy, if it's a busy spa, uh you've got either trichlor or dichlor being put in there, both of which are a little bit acidic. Um, a lot of times we see spas, the pH going very high all the time because we've got aeration and turbulence, which raises the pH a lot. It may be that if you've got a spa like that, it may not be used very much, and then or it may be used a lot, and they're putting a lot of chlorine in there, and the the chlorine level is actually lowering the the uh the pH and the alkalinity. And don't forget, um our bodies have a pH of about 7.45, believe it or not. Overall, blood system, everything, 7.45. So keeping the pH either direction 0.3, plus or minus from that is is okay. But when you get outside of that range, it can become irritating. So we're looking at 7.8 or 7.2 being a problem. So when you get to 7.2 or when you get to 7.8, you can have body irritation.

SPEAKER_00: 9:44

On both ends of the spectrum.

SPEAKER_01: 9:46

That's right. Um, and you combine that with a little bit of combined chlorine or chloramines, and chloramines, believe it or not, are are irritants, and you can smell them at 0.2 parts per million, which is the reason that we say that combined chlorine should not be greater than 0.2 parts per million, because it becomes an irritant at that level, and you can also smell it.

SPEAKER_00: 10:13

And so the best way to raise low pH. Now, I'll throw this out there. I've done this, and a lot of the members of my group, they'll go to Walmart and they'll buy 20 mule team borax and they'll put it into the raise the pH of the pool. And you're adding borease to the pool at the same time at some level, but what's the best way to raise the pH? I think the borax product, in my opinion, is a great way to do it if it's really low and you're wanting to raise the pH. But you wouldn't be using baking soda. That's a lot of people are selling that as something that raises pH. I know even on the bag of the baking soda, you know, if you buy the the 10-pound bag at Costco, it'll have a it says, you know, the raised pH, add this to the pool, but that's not that's a misnomer, right?

SPEAKER_01: 10:56

Yeah, it really is. Um bicarb, so that you can get a little bit of an understanding, the strongest solution you could make of bicarb would have a pH of 8.3. So that's the highest it can go. Even if you you put a whole bag of of bicarb in your spa, the pH isn't gonna go over eight point three. And you can see if your pH was already seven point two or seven point four, if you added some bicarb to the water, it's really not gonna change the pH very much. You know, because it's not very strong. You know, soda ash has a pH of 13. So when you add it, there's a big difference between 7.5 and 13. So it raised the pH a lot. But bicarb does not raise the pH unless the pH is very low. If the pH was say 6.8 and and you put in some bicarb, it's gonna raise the pH, but not not very much. If you if you added enough to get the alkalinity to the right spot, the pH would still be low. So um so you can't use bicarb to raise the pH. If you ever get the pH below uh about five, you can't put bicarb in anyway. It won't it won't raise the pH at all. Because below a pH of five, when you put bicarb in, it gases off as CO2. And so um so it doesn't work. In any case, I would not use bicarb to raise pH at all. Um you can use borax, it adds a little bit to alkalinity. Borax has a pH of about 9.2. So when you add it, it's it raises the pH more than bicarb would, but less than what soda might. Um and it doesn't appear to affect your alkalinity much, but as you might have guessed, you know, we make a an adjustment to the saturation index for cyanuric acid. There is also an adjustment you have to make to uh the saturation index for borate. If you do put borates in your pool, your alkalinity figure is uh your total alkalinity reading is actually lower than than you think it is.

SPEAKER_00: 14:00

Percentage uh number for that, like offhand?

SPEAKER_01: 14:03

Um no, it doesn't work that way. It does for cyanuric acid. We can use basically one-third, but because it's a buffer to keep the pH from going high, the higher the pH, the more it affects it. At a pH of 7.5, the if 50 parts per million of borate would only affect the reading by about six or seven parts per million. But as you get up to seven, eight, or eight, now it affects at about twenty. And if you get up above eight point two, it affects at about forty.

SPEAKER_00: 14:35

And we should also mention that soda ash also raises alkalinity as well as pH.

SPEAKER_01: 14:41

Yes, and it raises it to ounce per ounce, it raises it more than uh bicarb does.

SPEAKER_00: 14:48

So if you have a pool with low alkalinity and low pH, the so soda ash is perfect.

SPEAKER_01: 14:54

That's right. That's right. When when you need to raise both, use soda ash, and when you need to to just raise alkalinity, uh use bicarb. But don't forget that you can aerate to raise pH. Yeah. And so a lot of times I tell people, listen, if you're if your if your pH is low and your alkalinity is low, you can add just bicarb to get to the exact alkalinity that you want. And then aerate till you get to pH of seven, five, and you'll have a perfectly balanced pool.

SPEAKER_00: 15:29

Yeah. So if you have a hot tub that has a really low pH, let's say it's at six, and alkalinity is at 40, put some baking soda in there and then turn that thing on and let it run for a couple hours. That's right. That's right.

SPEAKER_01: 15:39

Put enough baking soda to get the alkalinity up to 80 or 90, and then and then turn the turn the aerator on, uh, you know, the blower and the and the jets and whatever. And in a spa, uh, you'll probably raise the pH up to 7.5 in about a half an hour.

SPEAKER_00: 15:59

Yeah.

SPEAKER_01: 16:00

It's really a short time.

SPEAKER_00: 16:02

And then I guess lastly, the lower the pH, I mean, I know the cyaneric acid is a big factor in the chlorine kill factor, but you mentioned that at the lower pH, it makes the chlorine, the killing part of chlorine more effective. So a pool at 7.6, technically, let's say the cyaneric acid level is in range at 50 parts a million, pool at 7.6 or 7.4, the chlorine will have a better killing ability than a pool at 8.0.

SPEAKER_01: 16:30

You know, probably not, because we used to we used to believe that all of the chlorine was, you know, subject to that that fraction that I told you, 50% HOCL and 50% uh OCL minus. But the problem is that when 97% of the chlorine is bound to bound to cyanuric acid, and you've only got three percent, it changes things a little bit because the concentration of cyanuric acid and the concentration of chlorine changes that 3% figure. It it almost doesn't matter as far as it being effective. The real important thing is to is to get the proper level of chlorine in there. So it doesn't necessarily affect the killing power of 7.5 versus 7.8. The killing power is not going to be that much different, but you need to have enough chlorine in there to prevent the algae. And again, it goes back to that percentage rather than doing what the pool stores say and keeping two to four parts per million of chlorine in the water, it doesn't always work. You know, two it is two to four, but you're gonna find in most cases that the minimum level needs to be nearer to four than it does two.

SPEAKER_00: 17:58

And so the guys that are obsessed about keeping the pH at 7.4, 7.6, they're pretty much it's not making a big difference. You know, I think in the old old days we're always taught that a high pH makes the chlorine less effective, but that's the old Yes, and we believe that because as the as the pH goes up, the effectiveness of the chlorine goes down.

SPEAKER_01: 18:20

Um so at a pH of of 7.8 or or 8.0, you've only got about 20% of the chlorine in the killing form and 80% in the non-killing form. That doesn't matter so much because of the influence of cyanuric acid and the concentration of chlorine and cyanuric acid. So um it it doesn't matter that much anymore. But we still need to balance the pool. It's not to say that you can keep a pH up around eight and and still have have good killing power and everything. You will, but you're gonna have bathers unhappy because we got above that 7.8 level where it starts to irritate bodies. So, you know, you don't want to run a pool at 7.8 because you're only you're right on the borderline of where the water now becomes bathers will notice the pH. Either they get they get itchy skin, they get irritated eyes, or something like that, because the pH is is 7.8 and all it needs to go is to 7.9, and now you irritate the bathers. You know, at 7.5, you've got 0.3 before you can have a problem.

SPEAKER_00: 19:34

If you're looking for other podcasts, of course you can go to my website, swingingpoolearning.com on the banner, click on the podcast icon. There'll be a drop down menu over eighteen hundred podcasts for you there. And if you're interested in the coaching program that I offer, you can learn more at poor coaching.com. Thanks for listening to this podcast. Take a rest of your week and God bless.