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How to Actually Find the Source of Algae in Your Pool

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Algae in a swimming pool is not always a “bad chlorine” story, and treating it that way can waste time and money. Some pools rarely see a bloom, while others fight green dust or mustard algae all season. The first step in effective pool algae prevention is figuring out the source: is it being introduced constantly by the environment, or is it taking hold because water care fundamentals are failing? Wind-prone yards, heavy pollen seasons, and nearby trees can load a pool with organics that feed growth. Shady surfaces and wall seams also give algae a place to settle, especially when brushing is skipped. A big clue is where the algae appears. If it keeps returning on steps, in a spa, along a deep-end corner, or behind ladders, you are likely dealing with low circulation “dead spots.” Those areas may not receive enough measurable free chlorine, even when the test at the surface looks fine. Poor mixing means sanitizer is not reaching the exact surfaces where algae attaches and grows. Return...
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Bob Lowry on Pool Service Rookie Mistakes

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New pool service pros often inherit “rules” like keeping free chlorine at 2–4 ppm and calling it good, then wonder why algae keeps coming back. A core mistake is not understanding how cyanuric acid (CYA) changes chlorine strength. With CYA in the water, most chlorine becomes bound and only a small fraction is immediately active as sanitizing hypochlorous acid (HOCl). Add in the way pH shifts HOCl versus OCl-, and the effective killing power can drop fast. That is why a pool can test “high chlorine” and still grow algae. If you run a pool service business, this is one of the most important pool chemistry concepts for consistent, algae-free results and fewer emergency cleanups. Once you accept that the active sanitizer is what matters, the free chlorine target has to scale with CYA. The practical field rule discussed is simple: keep free chlorine at about 7.5% of the cyanuric acid level to prevent algae. So if CYA is 100 ppm, free chlorine needs to be about 7.5 ppm, not 3 ppm. This refra...
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Bob Lowry on Dialing in Free Chlorine the Right Way

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Pools that “won’t hold chlorine” are one of the most common and expensive headaches in pool maintenance, especially for pool service pros trying to stabilize water fast. When someone says they’re adding two or three gallons of liquid chlorine a day to an 8,000 to 10,000 gallon pool and still reading near zero free chlorine, the first move is not panic dosing. It’s investigation. Chlorine demand usually has a cause: organics, contaminants, or active growth. Start by looking beyond the water test and into the yard, the deck, and the daily habits around the pool. Grass clippings, fertilizer drift, landscaping debris, and rain runoff dripping from dense vegetation all add organic load that chlorine must oxidize. Even well-meaning actions like washing the deck so dirty rinse water flows into the pool can wipe out chlorine overnight.   Once you suspect contamination, think like a detective and list every source of oxidizer demand. Heavy bather load can create big swings, especially ...
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Bob Lowry Breaks Down TDS in Pool Water

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Total Dissolved Solids (TDS) is one of the most ignored numbers in pool water chemistry, even though it quietly influences how water behaves. TDS simply means the total amount of dissolved material in the water, measured in parts per million, and it is not the same as visible debris or suspended solids. Modern pool service pros usually measure TDS with a digital meter that reads conductivity and converts that to a ppm estimate. That convenience is why it exists, because the old-school “total dissolved residue” method required evaporating a carefully measured sample and weighing what was left. The key takeaway for pool maintenance is that TDS rises as you add chemicals over time, and that rising baseline changes the way your test results and balance calculations perform. A practical way to think about TDS is the “kettle scale” analogy: keep boiling water away and you eventually see what was dissolved all along. In pools, the biggest contributors are often chloride and sodium. Every time...
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Bob Lowry on the Dangers of High CYA Levels

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Cyanuric acid (CYA), often called pool stabilizer or pool conditioner, is usually introduced as a simple shield that protects chlorine from sunlight. But the deeper story is what makes or breaks clear water: CYA changes chlorine effectiveness by binding most of the chlorine in the water and controlling how much active sanitizer is available at any moment. In this conversation, Bob Lowry explains why “normal” chlorine readings can be misleading, how CYA acts like a buffer in pool water, and why understanding the stabilizer to chlorine relationship is a cornerstone of reliable pool maintenance for service pros and homeowners alike.   The key insight is the equilibrium between free chlorine and chlorine bound to cyanuric acid. Once CYA rises above about 30 ppm, a very large percentage of chlorine becomes bound, leaving only a small fraction immediately active. That does not mean the chlorine disappears, it means it releases more slowly as the active portion gets consumed. The pra...
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Bob Lowry: The Truth About Persistent High pH in Pools

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Constant high pool pH is one of the most common pool water chemistry problems, and it usually is not “mystery water” at all. A persistent pH rise is often driven by carbon dioxide off gassing, which is controlled largely by total alkalinity (TA). When TA is high, the water is effectively overcarbonated, so CO2 wants to escape until it reaches equilibrium with the air above the pool. As CO2 leaves, the pH rises, which leads to the familiar cycle of adding acid, watching pH drop, then seeing it climb again. If you want stable pH, the strategy is less about chasing numbers and more about reducing the conditions that accelerate CO2 loss. The practical takeaway is to rethink alkalinity targets when you are dealing with chronic high pH. Many “standard ranges” for total alkalinity are too broad to solve real-world pH drift, especially in modern pools with lots of aeration. A target around 90 ppm TA can be a starting point, but if pH still climbs, lowering TA to 80 ppm or even near 70 ppm can ...
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All About Metals in Your Pool with Joe Laurino

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Metals in pool water are one of the most common reasons otherwise clean pools end up with ugly stains, tinted water, and frustrated customers. The key idea from this conversation is simple: sequestering agents help manage metals, but they do not remove them. Dissolved metal ions can stay in circulation and later oxidize from chlorine or oxygen, turning into solids that “plate out” on plaster, steps, and fittings. That is why a true pool metal removal approach matters, especially when draining is expensive or impossible. Joe Loreno explains how the Culator polymer works differently by binding metal ions while the polymer itself does not dissolve, letting you physically take metals out of the system.   To solve a problem, you also have to know where it starts. Common sources of pool metals include fill water and source water, pool equipment, certain pool chemicals, filter media, plaster and masonry materials, and metal parts in water features. Outside the pool, runoff can bring ...
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