But Why?

My father never explained anything he did. He just did it. T Navy frogman. T Farmer. Guitar player. T He moved through the world with a quiet certainty that never needed justification. You either understood what he was doing or you didn't. He wasn't gonna slow down to explain it either way. I spent most of my childhood trying to figure out why. Not just what he was doing, why. That question followed me everywhere. Into engineering, into the Navy, into a field laboratory in Kansas City, and a test kit that never lies. And every time I asked why in this industry, I found one of two things. A real answer, back to science, nothing.

Just happen. This episode is about the second day. It started somewhere older than that, somewhere quieter. My father played guitar. Not casually, he was exceptional. One of the finest players of his era, though he would never have said that about himself, and would have been genuinely annoyed if you said that about him. He played because it was the only place he could go where everything else got quiet for a minute. Where whatever he was carrying stopped making noise for an hour or so. I used to watch him play from across the room when I was a kid, and what I noticed even then was that he never played the same thing twice exactly the same way.

The song was the same, but the way he moved through it was different every time. Reading something in the room or in the moment or in the instrument itself that I couldn't hear yet. One night when I was about eight years old, I asked him why he played it differently. He looked at me for a second and said because it wants something different tonight.

Like I said, I was maybe eight years old. I had no idea what that meant. I've spent a long time figuring it out. A pool is like that. The chemistry gives you the framework, the data gives you the reading. Your job is to develop enough feel for the system to hear what it actually wants. Not what the chart says, not what the laminated page on the counter at the pool store says. What the system is telling you right now. That starts with asking why. About everything. Every rule, every target, every recommendation on that laminated page at the counter of the pool store in every state in this country.

Why does the industry say this? What is the actual mechanism and who benefits if you just accept the answer without asking? Three rules the industry has been repeating for decades, three whys that changed how I do this work. So let's go.

If you walk into any pool equipment showroom and talk to a salesperson about a pump upgrade, you'll hear some version of this. More horsepower, faster turnover, better circulation, premium equipment for a premium pool. And honestly, it sounds like common sense. More power equals better performance. It works for trucks, it works for lawnmowers, it works for just about everything else in a homeowner's life. Ask why.

Here's what a pump actually does. It has one job. It moves water through the filter at a rate that allows the filter media to do its job. That's it. The pump exists to serve the filter, not the other way around. And here's what happens when the pump is oversized. Water moves through the filter bed faster than the media can capture fine particulate. The contact time between the water and the filter media drops. Filter efficiency drops with it. You're moving more water and filtering it less effectively. The pool owner paid a premium for a piece of equipment that is actively working against the very thing it was purchased to accomplish.

Then there's the energy bill. An oversized pump running around the clock costs significantly more to operate. For worse filtration. Premium price, premium operating cost, inferior result. If someone sold you that in any other context, you'd want a refund and possibly have a conversation with your attorney. Then there's equipment wear. Excessive velocity through fittings, valves, and the filter itself creates erosion over time. Premature failure on equipment that was sold to you as a premium. The thing that was supposed to last longer turns out to have a shorter service life than a properly sized system would have delivered. I'm not going to tell you bigger is always wrong.

Sometimes bigger is exactly right, and the reason it's right has nothing to do with anything the salesperson told you. The exception is total dynamic head. And this is where the physics get genuinely interesting. Every pool system has a resistance to flow, pipe friction, fittings, valves, filter media, vertical elevation. If your equipment pad sits significantly higher than your pool water level, the pump has to work against gravity to pull water up to the equipment and push it back down. That vertical separation is called static head. It's real, it's measurable, and it does not care how nice your equipment pad looks.

Every pump has what engineers call a pump curve. It describes the relationship between flow rate and pressure across the operating range of that pump. As resistance in the system increases, flow rate drops. Every pump has a point where the resistance is high enough that flow effectively stops. You can only pump water up a hill so far. A pump that's perfectly sized for a flat installation with clean, efficient plumbing may be completely inadequate for an installation with significant vertical separation, or a plumbing configuration that looks like whoever installed it was paid by the fitting. I want to pause on that image for a second. Have you ever been to your favorite Italian restaurant?

You know the one, the really good place. The one you've been going to for years, the one where the red sauce has been simmering since sometime last Thursday and you can smell it from the parking lot? That chicken marsala that arrives at the table, and you briefly consider whether you even need other restaurants in your life anymore? The garlic bread that comes out of the kitchen warm, wrapped in foil, and the conversation at the table just stops. Nobody needs to talk. There's nothing to say. The garlic bread has made language unnecessary. You know that place.

Have you ever sit down at that restaurant, looked across the table at the people you came with, took a look at your bowl of spaghetti that's piled high and steaming and the sauce is that perfect deep red, and there's a little bitty fresh basil on the top, and you think, oh my god, this is going to be extraordinary. I cannot wait to eat this. This is one of the great moments of my life. Yeah.

I do not get that feeling when I pull up at an equipment pad that has been plumbed like a bowl of spaghetti from a gas station. Not even close. Elbows to elbows to elbows. Unnecessary tease, pipe runs that go sideways, then up, then back down, then sideways again, then back up, before finally arriving at the equipment looking completely exhausted from the journey. And occasionally I'm not making this up a piece of electrical conduit doing the job that pool pipe was supposed to do. If you heard episode one, you know exactly the kind of thing I'm talking about. If you haven't, go listen. Do it now. I'll wait.

Each one of those fittings adds resistance. Each one is a tax on flow that the pump has to overcome. That plumbing is strangling the system. And the homeowner wondering why their pool isn't circulating properly has absolutely no idea, because nobody told them that the plumbing their installer left behind is the problem. Nobody told them because the installer is long gone and the pool store doesn't make service calls. The water moving through that equipment pad is working as hard as it possibly can and getting a fraction of where it needs to go, which is exactly how you'd feel trying to eat that gas station spaghetti. Working hard, not getting much out of it.

Wondering how it even came to this. Here's how I find out what a system actually needs. My company performs what we call a dynamic flow audit. Pressure gauge on the discharge side of the pump, a vacuum gauge on the suction side. The delta between those two readings tells the story every time, without exception. A system with flow issues has head loss hiding in that delta. Could be partially clogged skimmer lines, could be undersized pipe, could be a plumbing configuration that would make a hydraulic engineer weep quietly into their coffee every morning. Whatever the cause, the gauges find it. That audit generates real diagnostic information. And it almost always generates downstream work and revenue.

Replumbing jobs, equipment pad streamlining, filter upgrades, proper pump sizing based on actual measured system resistance rather than a number on a sales floor brochure. The full physics behind all of this, pump curves, system curves, total dynamic head, Bernoulli and his theorem, Reynolds and his numbers, friction loss, whatever fitting actually costs you and flow rate, all of that deserves its own episode. One I'm genuinely looking forward to. Because the hydraulic engineering that governs pool circulation is the same engineering that governs industrial process flow. It connects some of my favorite physics to a Thursday morning field visit in a way that nobody else in this industry has ever explained.

Stay tuned for that one. For now, the right pump for your pool is the one sized to the actual resistance of your specific system. Measured, not guessed, not upsold. Who benefits from bigger is better? The dealer makes more on a larger pump. The installer upsells on the job. Neither one of them gets paid to explain contact time or filter design to the homeowner. The right answer takes engineering. The profitable answer takes a brochure. Nobody was lying, the wrong answer just happened to pay better. Ask why.

Why do you treat algae the way you treat algae? A pool turns green. And here's what happens next approximately a hundred thousand times every summer across this country. Pool owner calls the pool store. Pool store says shock it, add algae side, brush it, repeat. The pool owner follows the protocol, spends the money, does the work. And then wonders why it's taking so long. Ask why. Let's start with what algae actually is. And I want to spend a minute here because not all algae is the same thing, and that distinction matters more than the pool store protocol acknowledges. Green algae is by far the most common. It's free floating or wall clinging.

It turns the water cloudy green or coats the walls in a slippery film, most of the time both. The one that most pool owners have dealt with at some time at least once. Yellow algae, sometimes called mustard algae, clings to walls, steps, and shaded areas. It's significantly more chlorine resistant than green algae. It requires a higher free chlorine level to kill, and it comes back persistently if it's not addressed completely. Often it gets misidentified as dirt or pollen or sand sitting on the bottom, which costs time and money before anyone figures out what they're actually dealing with.

Black algae is the one that keeps people up at night. It's technically not algae at all, it's cyanobacteria. It establishes deep roots in plaster and grout and grows a protective layer on the surface that makes it extraordinarily resistant to sanitizers. You have to break through that layer physically with aggressive brushing before the chemistry can actually reach the organism underneath. It's the most stubborn, the most persistent, and by a significant margin the most expensive to remediate. And then there's pink algae, which also is not algae. It's a bacteria, seratia marsisans. It forms in corners, around fittings, in areas with low flow. It shows up frequently in vinyl pools, resistant to normal chlorine levels, and it has a talent for coming back in exactly the same spot if the underlying flow condition isn't addressed.

Four different organisms, four completely different mechanisms, four different treatment requirements and thresholds. One bottle of algae from the pool store applied without adequate free chlorine. That protocol doesn't distinguish between any of them. Neither does the label. Now, what does chlorine actually do to algae? It oxidizes the cell membrane, it disrupts metabolic function. At sufficient concentration relative to your CYA level, it kills effectively and efficiently. The 7.5% rule applies here exactly as it applies everywhere else. Below that floor, free chlorine is not doing meaningful work against algae regardless of what the meter reads. The number looks fine. The pool disagrees. Loudly. In several shades of green. Now, the algae question.

And I want to be fair here because the chemistry behind these products is real and it deserves an honest explanation before I tell you what I actually think about them. Algaicide works by disrupting algae cell membranes and metabolic pathways. Copper based products interfere with photosynthesis and enzyme function. Quaternary ammonium compounds, the quats, disrupt cell membrane integrity. Polyquats do the same thing with a different molecular structure and less risk of foaming and staining. The mechanisms are documented. The chemistry is legitimate. But here's what the label doesn't tell you. Algaicide applied to an active algae bloom in a pool with inadequate free chlorine is largely ineffective. The algae is reproducing faster than the algaicide can disrupt it.

You need free chlorine to do the primary kill first, always first. Algicide in that sequence is a follow-up tool, a preventative tool, not a primary weapon against an active bloom. Using algicide as your first response to a green pool is like trying to bail a sinking boat before you found the hole. You're working hard, you're doing something, the boat is still sinking. And here's the thing that I've been saying my entire career that I want to say directly on this show. The word algicide is deceptive. Side implies a kill mechanism. Pesticide kills pests. Herbicide kills weeds. Homicide, well, you know. The side suffix means to kill.

Algaide implies that it kills algae. It doesn't. Not effectively, not against an active bloom, not without adequate free chlorine doing the real work first. What algacide actually does is retard algae growth, slows it down, it prevents establishment under the right conditions. It's a preventative and a retardant, which means if I'm being honest about what the product actually does, it should be called algat, not algicide. That's not a clever line, that's just what the product actually is. And the name it was given implies something the product cannot deliver on its own. That gap between the name and the function is where a hundred thousand pools turn green every summer.

Now here's the other side of this. The pool scientific service vehicles, we don't carry any algae side, not a drop. We maintain free chlorine at the correct level relative to CYA. That gives algae no foothold to establish. And I genuinely cannot remember the last time I had a green pool outside of pulling a cover off in the late spring. Not because I found a better algae side, because I was solving the actual problem rather than putting a band-aid on the symptom. The actual problem is always the same. Free chlorine below the floor relative to CYA. Fix that and algae doesn't get a foothold. Don't fix that, and nothing on the shelf at the pool store is going to save you.

Who benefits from algae side as the primary treatment recommendation? High margin product moves in volume during the algae season. Gets recommended as the targeted scientific solution because it has a long name, an authoritative label, and a word on it that implies that it kills things. The pool owner who leads with algicide and follows with chlorine will need more algaicide more often. A green pool that should have been cleared in three days takes two weeks. Two weeks of a frustrated pool owner buying product at a pool store that recommended the protocol that produced the two-week timeline. That's not a conspiracy. It's a protocol built on a product name that overpromises, sold by an industry that profits from the repeat purchase.

Ask why. Why is 7.2 to 7.8 the right pH range? Here's the version of this story most pool owners have heard. Too low and the water burns your eyes. Too high and the chlorine stops working and the water feels like you're swimming in something you'd use to strip paint. Keep it somewhere in the middle and everybody goes home happy and nobody files a complaint. That explanation is true as far as it goes. It does not go very far. Ask why. Here's what pH actually governs in pool water. Two completely separate mechanisms. Both are critically important. They're almost never explained together, and both converging at the same time on the same number for completely different reasons.

The first mechanism sanitizer efficiency. Free chlorine exists in pool water in two forms hypochlorous acid, which is the active sanitizing form, the one doing the actual work, and hypochlorite ion, which is the considerably less motivated form. It does very little, but it shows up on your test kit and collects a paycheck. It doesn't contribute much to the actual job. The ratio between them is governed almost entirely by pH. At pH of 7.5, roughly half of your free chlorine is active HOCL. That number appeared in episode two and it hasn't changed since then and It won't. At a pH of 8.0, that fraction has dropped significantly. At a pH of 8.2, you're looking at something well under a quarter of your free chlorine doing meaningful work.

And at 8.5, you're roughly down to 9%. Your test kit reads the same free chlorine number across that entire range. Let me repeat that. Your test kit will read the same free chlorine number across that entire pH range. Same number to completely different water. A pool at a pH of 8.2 with 3 parts per million free chlorine has a fraction of the sanitizing capacity of a pool at 7.4 with 3 parts per million free chlorine. One of them is protecting the people swimming in it. The other one is providing a number that looks reassuring on a service log while the water quality fails to do its job.

The second mechanism, the LSI. PH is one of the six variables in the saturation index, and it's the one with the most leverage. A small pH movement produces a significant LSI shift. At low pH, the water becomes corrosive. It wants calcium carbonate, and it goes looking for it in whatever surface it's in contact with. Your plaster, your grout, your equipment. At high pH, water becomes scale forming. Calcium carbonate wants to come out of solution and deposit itself on everything within reach. Your plaster, your grout, your equipment. The 7.4 to 7.6 target, which is tighter than the industry standard of 7.2 to 7.8, positions the hypochlorous acid curve and the LSI simultaneously in their most favorable ranges.

That's why the target is what it is, not because of swimmer comfort, because two separate and independent chemistry mechanisms both behave best in that specific window at the same time. That's not a coincidence. It's physics. The eye comfort story is true. It's also the simplest version of the answer. The version that requires no chemistry to explain and no diagram to follow. It's the version that gets told in pool stores because nobody behind that counter has a financial incentive to walk you through hypochlorous acid dissociation equilibria and saturation index calculations on a Monday afternoon when there's a line out the door and everybody's pool is green.

The commercial interest here is subtler than the pump or the algae side. Loose pH management means more chemical intervention. pH up, pH down. You shock it when the chemistry goes sideways because pH drifted and took sanitization with it. Every one of those is a product sale. A pool owner who understands the mechanism manages pH with precision because they understand what's actually at stake. Precise management means fewer emergency interventions. Fewer emergency interventions mean less product purchased. The industry's financial interest is not in your pH being precisely managed. It's in your pH being approximately managed and occasionally wronged. And by occasionally, I mean most of the time. Ask why.

Three questions. Three rules that turned out to be incomplete at best and commercially convenient at worst. Here's what connects them. In every case, the explanation given to the pool owner is the simplest version of the answer. Not necessarily wrong exactly, just missing the mechanism that actually matters. And the missing mechanism is always the one that would change behavior in a way that costs someone in the supply chain money. Nobody was lying, the wrong answer just happened to be more profitable than the right one, and nobody stopped long enough to ask why. So it kept getting repeated. And repeated. That's how habit becomes knowledge. If you own a pool, asking why is the most useful thing you can do with this show.

You don't need a chemistry degree, you just need to refuse the answer because that's how it's always been done. The chemistry will give you an honest answer every time. The supply chain, not necessarily. If you're a pool professional, asking why is what separates a technician from a scientist. The science is not complicated, but you have to be willing to question what you were taught, test it against the chemistry, and update your practice when the chemistry wins. That is the job. The laminated page on the counter at the pool store is not the job.

Before I go, a couple of things. I have been hearing from you more than I expected if I'm being honest. Through the Ask John page, through Reddit, in Facebook groups and on Instagram and on X, through people I've been servicing for years who listen to the show now and want to understand what I'm actually doing when I'm standing at their equipment pad. The emails, the DMs, the comments, all of it pointing at the same thing. They want more than a Tuesday episode can give them. They want someone who will look at their actual numbers, their specific pool, their specific chemistry, and tell them exactly what it needs and how to fix it.

Not a general answer built for everyone, but a real answer built just for them. I've been reading every single one of those requests. It numbers in the hundreds, and I want you to know that I've heard you. I've been building something that answers every single one of those requests. Something that's going to be a complete game changer for pool owners and pool technicians alike. It has a name now. It's called the Chemist's Circle. I'm not going to tell you everything about it today, because it deserves more than a few sentences at the end of an episode about pump sizing and algae. What I will tell you is this.

It's coming. It's going to be exactly what you've been asking for. And when episode 11 drops on June 30th, you're going to hear everything. Stay close. One more thing before I go. Next Tuesday, I'm going to introduce you to someone. Someone I've been telling you about in pieces across the last few episodes without quite saying his name. The episode is called From Strawberries to Submarines to Swimming Pools. It's the episode this whole platform is built on, and after nine weeks of Tuesday mornings together, I think you're ready for it. That introduction is next Tuesday. And if you're a guitar player, like I am, I want to hear about your favorite guitar.

Send me the story through the Ask John page at PoolsScientific.com. I'm serious about that one. My father never explained why he played differently every time. He said because it wants something different. I was eight years old and I had absolutely no idea what that meant. I understand it now. A pool wants something tonight, not what the chart says, not what the pool store recommends, not what the equipment brochure promises. What the actual chemistry says right now, in this water, at this temperature, with this bather load and this history. You find that by asking why. The habit goes back further than this podcast, further than a nuclear shrink, further than the work.

It started in a room with a man in a guitar and a question I couldn't stop asking. A man I've been telling you about in pieces across the last few episodes without quite introducing him yet. Thank you for listening. If this episode gave you something useful, share it with someone who takes their pool seriously. Next Tuesday, from strawberries to submarines to swimming pools, and it's a good one.