Balance or Bust: Finding the Ideal pH with Eric Knight

Forget the old rule that outdoor pools must live at 7.4 pH. We dig into why cyanuric acid, not pH, is the dominant force behind chlorine strength in the sun, and how reframing your strategy around the FC-to-CYA ratio can reduce algae, cut costs, and protect your surfaces. With insights from industry committee work and modeling, we explain why a 20:1 CYA-to-free chlorine ceiling matters, why 30–50 ppm CYA often hits the sweet spot, and how to choose targets that keep chlorine working without drifting into overstabilized territory.

We also tackle a costly habit: aggressive acid dosing. Most techs are using far more acid than needed to move from 8.0 to 7.5, and that overcorrection hammers the Langelier Saturation Index, etches plaster, and invites oxidation. We walk through accurate acid calculations, the importance of pre-dilution, and circulation techniques that avoid “acid plunges” to the floor. Along the way, we separate the roles of pH and alkalinity, show how alkalinity drives acid demand, and spotlight calcium hardness as the quiet anchor that stabilizes LSI so your system doesn’t whiplash week to week.

Finally, we compare outdoor and indoor realities. Without CYA, indoor pools follow the classic rule where pH directly sets chlorine strength. Outdoors, stabilizer changes the game—so stop chasing numbers that don’t deliver. The payoff is fewer algae battles, stronger sanitation, and longer-lasting surfaces through a measured, data-first approach. If this perspective helps, subscribe, share the show with a colleague, and leave a quick review so more pros can rethink their chemistry playbook.

• Why eye pH claims mislead
• How CYA binds chlorine and alters strength
• The 20:1 CYA-to-free chlorine ceiling
• Targeting 30–50 ppm CYA for balance
• Acid overuse, LSI crashes, and surface damage
• Pre-diluting acid and correct dosing amounts
• Alkalinity as buffer and its components
• Calcium hardness as the quiet LSI anchor
• Indoor pools without CYA follow classic pH rules
• Why pH “bounce” often comes from bad aci

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Chapters

• 0:59 Welcome And Setup
• 1:02 Coaching Program Invitation
• 1:04 The Myth Of 7.4 pH
• 1:11 Chlorine Strength, pH, And CYA
• 1:15 The CYA-To-Chlorine Ratio
• 1:25 LSI Swings And Acid Overuse
• 1:29 Indoor Pools Versus Outdoor Rules
• 1:32 How Much Acid Do You Really Need
• 1:41 Damage From Acid Misuse
• 1:46 Alkalinity, Buffers, And pH Moves
• 2:01 The Quiet Buffer: Calcium Hardness
• 2:12 Why pH “Bounces” Back
• 2:15 Resources And Sign-Off

Transcript

SPEAKER_00: 1:50

Hey, welcome to the Fool Guy Podcast Show. This is the longest running industry podcast show. As after my test season, I've been doing this for nine years, and I thank the loyal listeners who have tuned in over those years. And today I'm going to continue my interview from 2020 with Eric Knight. He was formerly from Arenda and Hasa. He's now the executive director of Waterscape University. And in this episode, we're going to talk about the ideal Ph level. You'll find these episodes really relevant today. And again, I want to thank the loyal listeners who have tuned in throughout the seasons. Are you a full 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 swimmingpoollearning.com. And so the homeowners that are trying to keep their pH at 7.4 is pretty much something that you don't recommend with this new center. Yeah.

SPEAKER_02: 2:55

Yeah, it's it's kind of self-defeating because we've been taught, right? And another thing is I was a competitive swimmer. I hear it all the time that this conventional wisdom in the industry is, oh, well, you have to have a 7.4 to 7.6 because that's the pH of your eyes. That's not true. Uh a simple Google search will tell you that's not true. Now it is supposed to be the pH of your blood, uh, 7.4, but your eyes, depending on how hydrated somebody is, and I looked at sources like the World Health Organization, like not just uh Wikipedia here. Depending on the hydration level of the person, your eyes pH can range from the mid-sixes to the mid-eights, and that's a huge fluctuation in pH. And as a swimmer, I could never tell the pH of a pool. I could tell if there were disinfectant byproducts in there, I could tell if there were a lot of chloramines because that would be irritating. I could never tell a pH swing. So that that's a myth.

SPEAKER_00: 3:54

Um, so the biggest takeaway for the listener with this discussion here, with the relationship between the pH and chlorine. We know the old thinking is that the lower the pH, the more effective the chlorine. But now we've talked about throwing CY into the equation. So let's say that someone's cyaneric acid level is 100 in their pool. What would be something the takeaway from having the high cyaneric acid in the pool like we mentioned would make the chlorine less effective? Um and so the best way, in your opinion, to manage the pool is to have a lower cyaneric acid level and not to be overly concerned about keeping the pH within that small range that we've been taught, right?

SPEAKER_02: 4:34

Yes, that's a that's a good way to summarize it. So for instance, 100 parts per million stabilizer, like you just said, if you're trying to keep algae from growing in your pool and you're not doing proactive measures like removing phosphates, you have to have a minimum of 7.5% of your CYA to stave off algae and to prevent it. So that's 7.5 parts per million of free chlorine that you must maintain in order to stay ahead of algae. And that's that's the closest estimate that has been extrapolated from models. And we got that number from a guy named Richard Falk, who's on these committees. Uh, he's on the ad hoc committee for CYA. In fact, most of our information comes directly from him. Um, he's the guy who published that chart that I just showed earlier. So the CYA ratio, or the CYA to free chlorine ratio, according to that committee, should not ever exceed 20 to 1. 20 parts per million CYA for every one part per million free chlorine. If you go over that, you're considered overstabilized. My opinion, you don't ever want to go anywhere near that. So for a homeowner listening or a pool service guy, just make sure you're not overstabilized and you're below that ratio because you will get the sunlight protection you need at 30 to 50. Uh, but your chlorine will get used up a little bit faster. That's not necessarily from sunlight. That's because it's working faster to do its job. So uh, you know, it's a it's a bit of a trade-off, but that is a much more reliable strategy, I would say.

SPEAKER_00: 6:11

And so overfocusing on pH is probably not the way to do it if you wanted to balance the pool correctly.

SPEAKER_02: 6:17

Correct, because that fluctuation in pH is going to throw off your LSI too. If you're making big dips down to 7.2 and you know it's going to be coming back up to 8.0 by the end of the week, that's a dramatic difference. That's a huge swing on the LSI. I would much prefer that lower the pH to like 7.6 or maybe a stabilizer in their pool. And I'll be the first to tell you, I know that sounds really counterintuitive and it's it sounds very contrarian. Look at the data. We didn't publish the data. All I'm doing is I'm just the messenger. It won't impact your chlorine strength, provided you're not overstabilized with CYA. Let's not forget, there are a lot of pools that don't use any stabilizer, like indoor pools. On an indoor pool, pH absolutely controls the strength of the chlorine. So it's not like that lesson is false, it's that it gets overpowered because you have a stronger, uh, you know, basically a stronger variable in there called cyanuric acid. So it and it is, it's it's a it's kind of like a punch in the gut. It's how it was described to me by veteran pool guys who have been doing this their whole time. Let me ask you a question. Uh, on your pool route, you've been doing this for a long time and you really know your stuff. 20,000 gallon pool. You've treated a bunch of those, right?

SPEAKER_00: 7:38

Mm-hmm. Correct.

SPEAKER_02: 7:40

The pH is eight when you get there, which is very common because pH is going to climb. You want to lower it to 7.5. How much acid does that take?

SPEAKER_00: 7:48

Yeah, so it takes probably um a good half gallon, I would say, or close to that.

SPEAKER_02: 7:54

You know, vast majority of people, I would say nine out of ten at least around the country give the same exact answer half gallon to a gallon. In reality, it's more like a court. And most people don't know that. And that's not an indictment on you. But what's happened is people forget other factors. And so, in in reality, we got to measure the acid because if you are putting in a half gallon, that's way more acid than you need. And if you follow the arena app, half gallon of acid from an 80 pH in a 20,000 gallon pool actually drops your pH to more like 6.7 to 6.8, not 7.5. Well, what do you think that did to the LSI? This is how liners fade. This is how liners and fiberglass uh shells deteriorate. And for fiberglass, once that gel coat starts deteriorating, chlorine starts oxidizing it because it's opened up, which we're learning a lot more about that too. But especially for plaster pools, it you know, acid plunges to the bottom of the pool and you get an overcorrection locally, and it causes a real mess. And I like to say this is the truth, we don't get called to the good pools. I've only been doing this three and a half years, nobody's ever invited me to a good pool. It's always a problem pool. And I will tell you, the vast majority of the problems that I see have to do with acid being poured incorrectly or too much for a sustained amount of time, whatever it is. And it's because of this psychology that we have to keep lowering the pH every week. And and you kind of do, but not down to 7.4 or below. That means that habit needs to change, and we have to add acid correctly by pre-diluting it.

SPEAKER_00: 10:01

Now, I guess I can throw another variable in there since um we're talking about the pH and the effect on the water. Um, alkalinity. So it's a buffer to pH in the water. And I know that with cyaneric acid, you have to do the adjusted alkalinity. I've done uh a podcast on that one before also. Um so if the high alkalinity is really high in the pool, which in California we do have some pools with very high alkalinity out here, and if the alkalinity is really high in the pool, the cyaneric acid level, let's say it's in range in the pool, but the alkalinity is really high. When you add that muratic acid to the pool, doesn't the alkalinity buffer that in some ways?

SPEAKER_02: 10:41

It it will. Let me make sure I understand your question though.

SPEAKER_00: 10:45

Okay.

SPEAKER_02: 10:45

You're saying uh are you asking when you add acid to a pool, is alkalinity going to slow down the pH drop? Is that what it's yeah, it's like a buffer.

SPEAKER_00: 10:56

Well, um, you know, it takes the old rule of the old thinking, or maybe it's a standard thinking still, even without the adjusted alkalinity, is that if the alkalinity is at 200, it's gonna take more, it's gonna even if you put in a half a gallon of acid in that same 20,000 gallon pool, um, the pH is gonna bounce much quicker back up because of the alkalinity as a buffer in there, versus if the alkalinity was at 60, you add that acid in there, there's no real buffer in the water. I'm just trying to get a handle around the fact um adding cyanaric acid to the equation with the chlorine effectiveness, um, but I also want to also um see if the alkalinity level could also be a factor when you add that much acid to a pool.

SPEAKER_02: 11:40

Okay, I I understand what you're asking. Um so alkalinity, we've got to think of it as just a kind of a how much sort of question, as opposed to pH, which is an equilibrium that's kind of like a seesaw or it's it's a balance and it's constantly moving. Alkalinity is much more easy to control and to predict. So if you have a hundred parts per million alkalinity, when you measure total alkalinity, it includes things like hydroxide. Sorry, uh it includes bicarbonates, it includes carbonate alkalinity, it includes cyanurate alkalinity, which is what needs to be removed in order to get to the carbonate alkalinity for the LSI. Uh things like borates contribute to the buffering capacity, even phosphates could contribute. And the last two are in a smaller amount, but they still are significant enough that you can manipulate your pH up and down. But there's a different buffering agent that nobody talks about. And that's because it doesn't buffer pH directly, but it does buffer the LSI, and that's calcium hardness. People don't appreciate calcium hardness, but in reality, it's probably your best friend, provided it's not off the charts high. Um provides you a great foundation for a steady saturation index because it doesn't move. Like uh, if you ever look at the back of a TUMS, like if you ever take had indigestion and you take those little tablets of Tums, the key ingredient is calcium carbonate. And at the end of it, you know, dot dot dot dot dot, antacid. So calcium carbonate is an antacid. Well, that's what alkalinity is, it neutralizes acids. So when you're trying to say lower your pH from 8.0 to 7.5, your alkalinity determines how much acid that takes because you have to burn through more of it if the number's higher. So for instance, uh, I'm gonna do it on the Arenda app right now while we're on the phone, and I'm gonna set a 20,000 gallon pool from 8.0 down to 7.5, and I'm gonna start at 80 alkalinity. At 80 alkalinity, it takes 28.02 ounces of myriatic acid. 28 ounces. At 90 alkalinity, it's 31.5 ounces. So now you've gone up another three ounces. At 100 alkalinity, it's 35.02. And so you see the higher your alkalinity, the more acid it takes to do the same pH correction. That's because you have more of a buffering capacity you have to burn through in order to do that.

SPEAKER_00: 14:18

Got it.

SPEAKER_02: 14:19

Yeah, so you're you're absolutely right. But the pH bounce, like bouncing back, this is my opinion. This is not Arenda's opinion. This is uh just kind of a gut from what I've heard from customers. I don't think the bounce is because of the alkalinity. I think the bounce is because people aren't adding acid properly, because it's plunging to the bottom of the pool. It's etching, it's pulling out a 12.6 pH calcium hydroxide, and that's the cause of the bounce.

SPEAKER_00: 14:50

And if you're looking for more podcasts, of course, just go to my website, swimmingpoollearning.com, click on the podcast icon on the banner. That'll take you to a drop down menu of over 1800 podcasts there for you. And if you're interested in the coaching program that I offer, you can learn more at PoolGuideCoaching.com. Thanks for listening to this podcast. Have the rest of your week and God bless.