The Pools Scientific Podcast

John Cooper walks through building a personal pool care protocol based on your water, surface, season, and test results. Learn to read the numbers together, explain the reason behind each decision, and check what changed afterward. The goal is a practical page you can understand and update as your pool changes.

Show notes and free resources at PoolsScientific.com. Subscribe to the weekly email list for episode updates. Ebooks available at payhip.com/poolsscientific. Follow us on Instagram @poolsscientific24. The Pools Scientific Podcast is produced by Pools Scientific LLC — Elevated Pool Care Through Science and Technology.

Pool maintenance myths don't sound like myths. They sound like settled knowledge, because they've been repeated a thousand times. Repeated advice still isn't tested advice.

A listener closed an in ground vinyl pool in the mid Atlantic, balanced it to a slightly positive LSI calculated at 40°F (4°C), and asked how to add chemicals under the cover, with no circulation, if the water drifted over the winter. The most common answer was don't. John takes the four ideas behind that answer one at a time: you'll stain the liner, cold stops the chemistry, nothing bad ever happened, and you can fix it all at opening.

Then the chemistry. Cold water holds more calcium carbonate than warm water, so as a pool cools it becomes more aggressive toward any surface that contains calcium. You'll hear how far the LSI drops from temperature alone, what rain and snowmelt through a mesh cover do to calcium and alkalinity, and what aggressive water does to plaster, vinyl liners, and fiberglass gel coat over a winter.

And the answer to the listener's question: yes, you can. Water temperature decides the job, a monthly six number panel shows which way the water's moving, pH is the first move in cold water, and everything goes into a bucket of pool water before it goes in the pool. In winter the LSI almost always drifts low, so the correction is usually to bring pH up, not down.

If you want a chemist to look at your winter numbers with you, that's what the Chemist's Circle is for. Everything about it is at poolsscientific.com.

Show notes and free resources at PoolsScientific.com. Subscribe to the weekly email list for episode updates. Ebooks available at payhip.com/poolsscientific. Follow us on Instagram @poolsscientific24. The Pools Scientific Podcast is produced by Pools Scientific LLC — Elevated Pool Care Through Science and Technology.

Winter is hard on a pool, and not all of it is explained. This episode sorts what can go wrong under the cover into three piles: Known, Theory, and Shrug.

John Cooper starts with the calcium crystals that appear on some plaster pools in spring and gives both published explanations a fair hearing, from Orenda Technologies and onBalance. Then winter dust, gypsum, the odd formations on drain covers, and one pool that opened with a layer of white dust and a pH of 9.2.

Then the damage that is completely preventable. What moving ice does to a sun shelf and the waterline tile, how far to lower the water level and why, and how to drain an attached spa, especially one sitting above the pool, so it makes it to spring in one piece.

Real answers for real pools. No guessing.

Show notes and free resources at PoolsScientific.com. Subscribe to the weekly email list for episode updates. Ebooks available at payhip.com/poolsscientific. Follow us on Instagram @poolsscientific24. The Pools Scientific Podcast is produced by Pools Scientific LLC — Elevated Pool Care Through Science and Technology.

Your hot tub is not a small pool, and treating it like one is where most of the trouble starts. 

In this episode, John walks through why a tub is a different animal: more bathers per gallon, water held at 104 degrees Fahrenheit (40 degrees Celsius), and nowhere for anything to go. 

We cover bromine vs chlorine and how to choose, why dichlor, the jar most pool stores hand you for a spa, quietly builds cyanuric acid until the sanitizer stops doing its job, and what the CDC says about Legionella and Pseudomonas.

Then hot water and the Langelier Saturation Index, total dissolved solids, equipment by tub type, and the biofilm hiding in the plumbing. 

You’ll leave with a standard you can explain, number by number. 

Show notes and free resources at PoolsScientific.com. Subscribe to the weekly email list for episode updates. Ebooks available at payhip.com/poolsscientific. Follow us on Instagram @poolsscientific24. The Pools Scientific Podcast is produced by Pools Scientific LLC — Elevated Pool Care Through Science and Technology.

Winter pool maintenance is where most pool damage starts, and almost nobody does it. 

Once the cover goes on, the water sits against the plaster, gelcoat, or vinyl liner for about six months, and cold water changes the chemistry in ways the summer rules don’t cover. 

John walks through what happens under the cover, why winter pool chemistry runs on the LSI instead of the in season numbers, and what a pool closing kit leaves out. 

You’ll hear what causes plaster etching in winter, why so many pools open green in spring, and the month by month plan for testing pool water in winter, from October closing through March. 

If you’ve wondered how to winterize a pool so the surface survives, start here. 

A note on this episode: Clarified

In Episode 26 I said the non-chlorine shock in a winter kit throws off the free chlorine test. More precisely, MPS mostly shows up as false combined chlorine. If you have used it and your combined chlorine reads high, do not shock against that reading.

Show notes and free resources at PoolsScientific.com. Subscribe to the weekly email list for episode updates. Ebooks available at payhip.com/poolsscientific. Follow us on Instagram @poolsscientific24. The Pools Scientific Podcast is produced by Pools Scientific LLC — Elevated Pool Care Through Science and Technology.

Pool plaster mottling is one of the most common complaints in new pool construction, and the industry's standard explanation, installer error or bad water chemistry, is usually wrong. 

The real cause is calcium hydroxide migration during cement cure, and it has been a solved problem in commercial concrete construction since the 1950s. The pool industry just never picked it up.

This episode covers the full mechanism: how Portland cement produces calcium hydroxide as a hydration byproduct, why it migrates to the surface, what it does when it gets there, and how the LSI determines whether your water is accelerating that process or allowing the plaster to stabilize.

The fix exists. It's documented. It's been in use in other industries for decades. This episode explains why your pool contractor has almost certainly never mentioned it.

Show notes and free resources at PoolsScientific.com. Subscribe to the weekly email list for episode updates. Ebooks available at payhip.com/poolsscientific. Follow us on Instagram @poolsscientific24. The Pools Scientific Podcast is produced by Pools Scientific LLC — Elevated Pool Care Through Science and Technology.

Pool plaster mottling gets blamed on your water chemistry almost every time. This episode asks a different question. 

What if the uneven gray discoloration was decided before the pool ever held a drop of water? 

We get into the science of new pool plaster problems, and what pool plaster warranty coverage actually protects you from, and what it does not. 

If your plaster is showing discoloration and mottling in the first few years, you are going to want to hear this one before your next call to the builder. 

Show notes and free resources at PoolsScientific.com. Subscribe to the weekly email list for episode updates. Ebooks available at payhip.com/poolsscientific. Follow us on Instagram @poolsscientific24. The Pools Scientific Podcast is produced by Pools Scientific LLC — Elevated Pool Care Through Science and Technology.

Pool metal stains rarely come from just one source, and this episode walks through the real chemistry behind them. 

John covers where metals and minerals actually enter pool water, why iron, manganese, and copper stain differently, and why calcium and magnesium follow the same solubility rules everyone assumes are unique to metals. 

He breaks down the difference between a sequestrant and a chelator, walks through a rare copper cyanurate case that took fifteen drain and refill cycles to correct, and explains whether salt water is actually corrosive at pool concentrations. 

The episode closes with a full, step by step remediation protocol for anyone dealing with an active metal stain right now, including when algaecide is the right call and when it isn't. 

If you've ever stared at a purple pool and had no idea why, this one's for you. 

Show notes and free resources at PoolsScientific.com. Subscribe to the weekly email list for episode updates. Ebooks available at payhip.com/poolsscientific. Follow us on Instagram @poolsscientific24. The Pools Scientific Podcast is produced by Pools Scientific LLC — Elevated Pool Care Through Science and Technology.

Closing day is the last time anyone touches your pool's chemistry until spring, and most closing checklists skip the one thing that actually matters: what happens to that water for the next five months. 

This episode covers pool closing chemistry by pool type, since winterizing an above ground pool, winterizing an inground pool, vinyl liner pool winterizing, fiberglass pool closing, and plaster pool winterizing each carry a different physical risk, not just a different checklist. 

From the water level rule that protects a vinyl liner's own shape, to why a fiberglass shell depends on its own water as ballast, to the buffer that lets plaster forgive a bad winter and the two ways that forgiveness runs out, this is the chemistry most closing guides leave out entirely. 

Four companion guides, one for each pool type, are linked in the show notes for the complete protocol. 

Show notes and free resources at PoolsScientific.com. Subscribe to the weekly email list for episode updates. Ebooks available at payhip.com/poolsscientific. Follow us on Instagram @poolsscientific24. The Pools Scientific Podcast is produced by Pools Scientific LLC — Elevated Pool Care Through Science and Technology.

Why does that sharp chemical smell at the pool mean your chlorine is losing, not winning? 

This episode breaks down the real chemistry behind combined chlorine and chloramines, the actual mechanism behind the seven and a half percent chlorine-to-cyanuric-acid ratio, and why a fixed LSI range can turn against your pool's plaster and equipment without warning. 

Includes a real two-year, zero-CYA field experiment on salt pools, and why some of the most repeated advice at the pool store counter was never built for your specific water in the first place. 

This one's about building the kind of pool chemistry confidence that doesn't depend on trusting whoever's behind the counter, knowing your own water well enough to trust yourself instead. 

A note on this episode: Clarified

I want to add some context to one part of this episode. The audio stays as it is, and this note is the clarification.

Low free chlorine with no CYA (about 13 minutes in). I described salt pools running with no CYA, some holding free chlorine as low as half a part per million, and I said none of them had turned green. That is what I saw in those pools, and it is a field observation, not a standard to follow. Clear water tells you the pool isn't growing algae. It doesn't tell you the water is disinfected, because the germs that make people sick don't turn a pool green. The CDC's Model Aquatic Health Code sets 1 part per million free chlorine as the minimum for public pools at all times, and calls for more when CYA is present.

My own rule is a floor of 1 part per million free chlorine when CYA is low or zero. When there is CYA, I keep free chlorine at 7.5 percent of your CYA level or higher. For a public pool, the health department's numbers come first.

Thank you for listening, and for holding me to a high standard.

Show notes and free resources at PoolsScientific.com. Subscribe to the weekly email list for episode updates. Ebooks available at payhip.com/poolsscientific. Follow us on Instagram @poolsscientific24. The Pools Scientific Podcast is produced by Pools Scientific LLC — Elevated Pool Care Through Science and Technology.