Most cloudy-water calls aren't a mystery.
Most South Bay homeowners who reach out about green water, itchy eyes, or a pool that refuses to clear up aren't dealing with something exotic. They're dealing with water that's out of balance. Understand what the four key numbers actually do, and your chlorine works harder, your equipment lasts longer, and your chemical use tends to level out across a season.
Here's what each pillar does and what to do about it.
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pH: The Number That Affects Everything Else
pH measures how acidic or basic your pool water is, on a scale of 0 to 14. Seven is neutral. Pool water should sit between 7.2 and 7.8, with 7.4–7.6 being the sweet spot most experienced technicians aim for.
Why does it matter so much? Because pH controls how effective your chlorine is. Even slightly above the ideal range, chlorine loses a significant portion of its sanitizing power—it's still present in the water, but it's not doing the job. You could be dosing consistently and getting very little germ-killing effect. On the low end, water below 7.2 is acidic enough to corrode metal fittings, etch plaster or fiberglass surfaces, and irritate swimmers' eyes and skin.
In the South Bay, pH tends to drift upward. This happens naturally because of bather load, sunlight, and the CO₂ your pool loses as the water moves. A little muriatic acid—added carefully and slowly, never poured directly onto a surface—brings it back down. Soda ash raises it when it drops too low.
Test your pH at least twice a week during swim season. It moves faster than most people expect.
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Total Alkalinity: pH's Shock Absorber
Total alkalinity (TA) measures how well your water can resist sudden changes in pH. Think of it as a buffer—it keeps pH from swinging wildly every time rain falls, a kid cannonballs in, or you add a chemical.
The target range is 80 to 120 ppm (parts per million—a standard way of measuring dissolved substances in water), though some plaster pools do well toward the higher end of that range.
When TA is too low, pH becomes erratic. You'll correct it one day and find it's bounced somewhere else two days later. When TA is too high, pH becomes stubborn—it locks up and resists adjustment no matter what you add. Both are frustrating, and both are avoidable.
Raise low alkalinity with sodium bicarbonate (essentially plain baking soda). Lower high alkalinity with muriatic acid, but do it gradually and in small doses. It can take several treatments over a few days to bring high alkalinity down without overcorrecting.
A reliable rule of thumb: always test and adjust alkalinity before you adjust pH. They're connected, and fixing alkalinity first makes the pH correction easier and more stable.
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Chlorine: Your Pool's Main Line of Defense
Chlorine is the sanitizer—the chemical that kills bacteria, algae, and other organic contaminants. But not all the chlorine in your pool is working at any given moment.
There are two forms to know:
- Free chlorine (FC): The active chlorine available right now to sanitize.
- Combined chlorine (CC): Chlorine that has already bound to contaminants and is essentially spent. High combined chlorine is what causes that sharp "pool smell" people often mistake for too much chlorine—it's actually the opposite.
The target for free chlorine is 1 to 3 ppm for most residential pools. Salt water pools—which use a salt chlorine generator to produce chlorine on-site rather than requiring you to add it manually—generally run in the same range. The generator automates the production; the target doesn't change. Hayward and Pentair both make widely used salt systems, and output is adjustable based on your pool's demand.
Every pool burns through chlorine differently. A shaded backyard in Saratoga will hold chlorine much longer than an open pool in Los Gatos or Willow Glen getting full afternoon sun. Bather load, organic debris, and sun exposure all factor in. Pay attention to how your pool actually behaves before you settle on a dosing routine.
If free chlorine consistently won't hold—you add it and it disappears quickly—test for combined chlorine and consider shocking the pool. Shocking means adding a large dose of chlorine (or a non-chlorine oxidizer) to burn off combined chlorine and reset the water. After a heavy storm, a pool party, or any event that dumps a lot of organic material into the water, a shock is a smart move.
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Calcium Hardness: The One People Forget About
Calcium hardness (CH) measures how much dissolved calcium is in the water. Most homeowners ignore it until something goes wrong—and by then, the damage is already under way.
The target range is 200 to 400 ppm.
Water always wants to be in equilibrium. If it's low in calcium, it will pull calcium from wherever it can find it: your plaster, your grout, your heat exchanger. The result is a pitted, etched, rough surface and equipment that wears out faster. This is called aggressive water, and it's particularly hard on heaters. The heat exchanger—the component that actually heats the water—is expensive to repair or replace when corrosion has been working against it. Raypak, Pentair, Hayward, and Jandy all make residential heaters, and none of them are easy on a repair budget when the water has been the problem all along.
If calcium is too high, the water is over-saturated and will deposit the excess somewhere—usually as white scale on your tile line, inside your filter, or on your salt cell. If your fill water runs on the harder side, as it often does in parts of the South Bay, high calcium is likely a more frequent concern than low calcium.
Raising calcium is straightforward: add calcium chloride. Lowering it is harder. The most reliable method is a partial drain and refill with lower-mineral water, which isn't always simple if your fill water is also mineral-heavy. A professional water test can tell you exactly where you stand before you commit to draining anything.
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How the Four Numbers Work Together
Here's what most pool guides skip: these four parameters don't operate in isolation. A change in one affects the others.
The Langelier Saturation Index (LSI) is a formula that combines all four readings—plus water temperature—into a single number that tells you whether your water is balanced, aggressive, or scale-forming. Negative LSI values point toward aggressive water; positive values point toward scale-forming water. A slightly positive reading isn't automatically a problem—the goal is to stay as close to zero as practical, since temperature and other variables shift the index over the course of a season.
You don't need to calculate this by hand. Good liquid test kits give you the individual numbers, and any experienced pool service technician can run the LSI for you. What matters is understanding that keeping all four numbers in range isn't about hitting isolated targets—it's about keeping them in balance with each other.
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What to Do This Week
- Test your water today. Use a quality liquid test kit or take a sample to a pool supply store for a full panel—pH, total alkalinity, free chlorine, and calcium hardness. Test strips give a rough read; liquid reagent kits are more accurate.
- Start with alkalinity. If it's outside the 80–120 ppm range, adjust it first before touching anything else. Then retest pH and adjust as needed.
- Check your free chlorine and note when it drops. If it falls fast between tests, consider your pool's sun exposure, swimmer load, and debris. Adjust your dosing schedule to match how your pool actually behaves, not how you wish it behaved.
- Look at your tile line. White crusty buildup is a sign of high calcium or high pH. A rough or pitted plaster surface can suggest the opposite. Either one is worth addressing before it gets worse.
- Call a pro if the numbers keep moving on you. If you're correcting the same problem week after week without it sticking, there's usually an underlying reason—fill water chemistry, a malfunctioning salt cell, or a dosing schedule that doesn't match your pool's actual demand. We service pools across Campbell, San Jose, Los Gatos, Willow Glen, and Saratoga, and we hold a California C-53 Pool and Spa Contractor license. Stubborn water chemistry is worth a second set of eyes.
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Balanced water doesn't mean perfectly still water. It means water that stays within a stable range week to week without requiring heroic corrections. Once you have a baseline and a rhythm, maintenance gets simpler, your equipment stays healthier, and the pool looks the way it should: clear and ready to use.
If you're not sure where your water stands right now, that's the first thing to find out. Everything else follows from there.