Why Is My Pool Cloudy? 7 Causes and How to Fix Each One

Cloudy water is one of the most common things a pool owner searches for, and the good news is it's rarely an emergency. Cloudiness means something is suspended in the water instead of dissolved or filtered out: dead algae, fine dirt, body oils, or mineral particles too small for your filter to catch yet. The fix depends entirely on which one it is, so working through the causes in order of likelihood will get you to the right answer faster than guessing.

1. Filtration isn't keeping up

Before you touch a single chemical, rule out the equipment. A filter that isn't running long enough, isn't running at all, or is clogged can't clear anything, no matter how perfect your chemistry is. This is the single most common cause of ongoing cloudiness and the easiest to check.

• Check the pump timer or automation schedule. Most pools need 8-12 hours of circulation a day, more in hot weather or after a party or heavy rain.
• Look at the filter pressure gauge. If it's climbed 8-10 PSI above its clean baseline, it's time to backwash (sand or DE filters) or hose off the cartridge.
• Confirm the pump basket and skimmer baskets aren't packed with debris, which restricts flow even when the pump sounds fine.
• If you recently added a lot of chemical or algaecide, run the filter longer than usual for a day or two while it catches up.

2. Free chlorine is too low

Once filtration checks out, chlorine is next. Free chlorine below the ideal 1-3 ppm range (acceptable range 1-4 ppm) lets algae and bacteria get a foothold, and a light, early algae bloom often shows up as a dull, hazy cloudiness before the water turns visibly green. Test your free chlorine first; if it's low, that's usually your answer.

Raising free chlorine with liquid chlorine follows a standard rule of thumb: about 1 gallon of ~12.5% liquid chlorine raises roughly 10,000 gallons of water by about 10 ppm. Cal-hypo shock follows a similar ballpark, roughly 1 lb per 10,000 gallons for about a 9-10 ppm rise, though the exact percentage varies by product, so check the label. These are estimates, not exact doses, so add chemical gradually and retest a few hours later rather than dumping in a guess and hoping. Skimmer's chlorine calculator can work out a dose for your specific pool size if you'd rather not do the math by hand.

3. pH or total alkalinity is out of range

Water balance problems don't just make chlorine less effective, they can cloud the water directly. High pH pushes calcium and other minerals toward the edge of what the water can hold in solution, and once they start dropping out, you get a fine, milky cloudiness rather than a dramatic change.

If pH is high, bring it down before doing anything else, since a lot of other chemistry problems get easier to diagnose once pH is back in range. If total alkalinity is also off, correct that first, it tends to stabilize pH so you're not chasing a moving target.

4. Calcium hardness is too high

If pH and alkalinity both test fine but the water still has that milky, slightly gray look, check calcium hardness. Above roughly 400 ppm, calcium can start precipitating out of solution as tiny particles, especially when combined with warm water or a high pH swing. This is more common in hard-water regions or pools that have been topped off repeatedly with hard tap water over a long stretch without a partial drain.

There's no simple chemical to lower calcium hardness the way there is for raising it. The practical fix is diluting the water, draining and refilling a portion of the pool with fresh water, which is worth confirming against your specific test numbers before you do it.

5. Early-stage algae

Cloudy water that has a faint green, yellow, or brown tint, especially combined with low free chlorine, is often algae before it's visibly "a green pool." Algae blooms don't jump straight from clear to green; there's usually a hazy in-between stage. A shock dose (breakpoint chlorination) is the standard response: roughly 10 times your combined chlorine reading, with most pool professionals recommending a minimum shock dose of around 10 ppm free chlorine even if combined chlorine reads low or wasn't tested.

• Test combined chlorine (the difference between total and free chlorine) to gauge how far along it is.
• Shock in the evening so sunlight doesn't burn off the chlorine before it can work.
• Run the filter continuously for 24 hours or more after shocking, and brush the walls and floor to knock loose algae into the water column where the filter can catch it.
• Retest free chlorine the next day. If the water hasn't visibly improved within 24-48 hours, another shock dose is usually the next step.

6. Fine particulates the filter can't quite catch

Sometimes chemistry and filtration both check out fine, but the water stays hazy anyway. This usually means the particles suspended in the water are simply too small for your filter media to trap efficiently, often after a dust storm, heavy pollen, sunscreen and body-oil buildup from a busy pool day, or a fine mineral cloud left over from a chemical dose. A clarifier or flocculant product can help here: clarifiers coagulate small particles into bigger ones your filter can catch, while flocculants drop everything to the bottom for a vacuum-to-waste. Follow the product label closely, since flocculants in particular require draining the settled material rather than filtering it out.

7. Cyanuric acid (stabilizer) has drifted too high

This one is more indirect. Cyanuric acid protects chlorine from breaking down in sunlight, with an ideal range of 30-50 ppm and an acceptable range of 20-80 ppm. When it climbs well above that, usually from repeated use of stabilized chlorine tablets without ever diluting the water, it can suppress how effectively your free chlorine actually sanitizes, even when the free chlorine number itself looks fine on a test strip. The practical effect is water that stays hazy or algae-prone despite chlorine readings that look acceptable on paper. If cyanuric acid is high, a partial drain and refill is generally the only real fix, and switching to unstabilized liquid chlorine for a while can keep it from climbing again.

Putting it together: a quick diagnostic order

If you only remember one thing from this article, remember the order: check filtration and run time first, then free chlorine, then pH and total alkalinity, then consider calcium hardness, algae, particulates, and cyanuric acid in roughly that order of likelihood. Most cloudy pools resolve at one of the first three steps. Logging each test as you go, rather than relying on memory, makes it much easier to tell whether a fix is actually working or whether you're chasing the wrong cause. This is exactly what Skimmer's water log is built for: track each reading, see the trend, and know within a day or two whether your fix is holding.