You’re standing by the pool, staring at the water. It looks... fine? Maybe a little dull. But the "Low Salt" light is blinking on your control panel, even though you just dumped four bags of salt in there last week. Honestly, it’s frustrating. You check the chemistry, and the chlorine levels are basically non-existent. This is usually the moment most pool owners realize they need to peer inside that translucent plastic housing.
So, what does a dirty salt cell look like when it’s actually causing problems?
It’s not usually "dirt" in the way we think of mud or grime. Instead, you're looking for a specific type of mineral buildup. If you pull that cell out and look through the grid, you’re likely to see something that looks like dried toothpaste or flaky white chalk wedged between the metal plates. It’s calcium. Specifically, calcium carbonate. When it gets bad, it looks like a miniature coral reef has decided to take up residence inside your plumbing.
The Visual Anatomy of a Scaled-Up Cell
When people ask what does a dirty salt cell look like, they expect a little bit of dust. What they get is a rock formation.
Take a look at the titanium plates inside the unit. In a healthy, clean cell, those plates are dark, sleek, and have clear gaps between them. You should be able to see straight through the cell like a window with blinds. But when things go south, you’ll notice white, crusty deposits. Sometimes it’s just a light dusting on the edges. Other times, the buildup is so thick that it bridges the gap between two plates, essentially short-circuiting the electrolytic process.
It’s sort of gross. It looks like hard water stains on a showerhead but magnified by a hundred. If you see chunks that look like crumbled feta cheese sitting at the bottom of the housing, your cell is screaming for a localized acid bath.
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There’s a nuance here, though. Not all "dirty" cells look white. Depending on your local water chemistry—shoutout to those of you with high iron or copper—the scale might look slightly tan, gray, or even a weird rusty orange. If you see dark spotting or "pitting" on the plates themselves, that’s not dirt. That’s permanent damage to the ruthenium coating, which is a much bigger (and more expensive) problem than just some scale.
Why Does This Even Happen?
Chemistry is a fickle beast. Inside that cell, the process of electrolysis creates a very high pH environment right at the surface of the plates. This is the "perfect storm" for calcium to fall out of suspension and stick to the metal.
If your pool water has high Total Alkalinity or if your Calcium Hardness is off the charts (looking at you, Arizona and Florida pool owners), the scale will grow faster than you can scrub it. It’s a literal physical barrier. The salt water can't hit the plates, so the chlorine stops being made. You end up with a "dirty" cell that is functionally useless, even if the electronics are working perfectly.
Variations of "Dirty" You Might Encounter
It’s not always white flakes. Sometimes, a dirty cell looks like it’s been infested by a swamp. If you have poor flow or the cell hasn't been running, you might see actual organic debris—pieces of leaves, hair, or even small sticks—wedged in the grid. This happens if your filter grid is breached or if you've been running the system without a pump basket.
- The "Bridge" Effect: This is the most common visual. White crust bridges the 1/8th inch gap between plates.
- The Peeling Paint Look: Sometimes the scale doesn't look like rocks; it looks like the plates are peeling. This is often just very thin, sheet-like scale.
- The "Blue-Green" Tint: If you see blue or green crystalline structures, you’ve likely got copper issues. This often comes from using cheap algaecides or from a heat exchanger that’s corroding.
Don't Trust the "Self-Cleaning" Myth
Most modern cells, like those from Hayward or Pentair, have a "reverse polarity" feature. Basically, the system flips the electrical charge to blow the scale off the plates. It’s clever. But it isn't magic.
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If your saturation index (LSI) is way out of whack, the self-cleaning cycle can't keep up. You’ll still end up with a cell that looks like it’s been dipped in plaster. Honestly, relying solely on self-cleaning is how most people end up killing their cells prematurely. You still need to do a manual inspection every three months. Just unscrew the unions and peek inside. It takes two minutes.
How to Tell if it's Dead or Just Dirty
This is where people get tripped up. A cell can look "clean" but still be "dirty" in a way that isn't visible to the naked eye. If the precious metal coating on the plates has worn off, the cell won't produce chlorine.
Look at the edges of the plates. Are they square and sharp? Or do they look rounded and "eaten away"? If they look thin and brittle, no amount of cleaning will save it. You’re looking at a replacement. On the flip side, if the plates look thick and the only thing you see is that white, chalky bridges, you’re in luck. A simple soak in a diluted muriatic acid solution (usually a 4:1 or 10:1 ratio depending on who you ask) will fizz that scale right off.
Watching the acid react with the calcium is actually pretty satisfying. It bubbles like a middle school science project. Once the bubbling stops, the scale is gone, and the plates should look dark and clean again.
The Real-World Consequences of Ignoring the Crud
If you ignore what a dirty salt cell looks like, you aren't just losing chlorine. You're stressing your power center. The control board has to work harder to push current through that mineral buildup. I’ve seen plenty of $500 control boards fried because the owner didn't want to spend twenty minutes cleaning a $150 cell.
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It’s also a safety thing. A dirty cell often leads to "chlorine demand" issues where the water looks clear but isn't actually sanitized. You go for a swim, and the next day everyone has itchy skin or red eyes because the combined chloramines are through the roof. All because of some calcium on a metal plate.
Action Steps for the Weekend
Don't wait for the "Inspect Cell" light to turn on. Those sensors are often reactive, not proactive.
First, turn off the pump. This is non-negotiable unless you want a face full of pressurized salt water. Unscrew the cell from the plumbing. Hold it up to the sun. If you can't see clear, unobstructed paths between every single plate, it’s dirty.
If you see that signature white crust, grab a plastic bucket. Never use metal. Mix your water first, then add the muriatic acid—always acid into water, never the other way around unless you enjoy chemical splashes. Submerge the plates but try to keep the plastic "plug" end dry if possible. Let it sit until the fizzing stops. Rinse it with a low-pressure garden hose.
Check your Calcium Hardness levels immediately after. If your water is "hard," you might need to add a sequestering agent to prevent the scale from coming back in two weeks. This keeps the minerals in solution so they don't stick to the hot plates of your salt generator. Keep your pH between 7.2 and 7.6; high pH is the fastest way to turn a clean cell into a dirty one.
Once the plates are dark and the gaps are clear, screw it back in and watch your chlorine levels bounce back. It's one of those maintenance tasks that feels like a chore but saves you a massive headache during the peak of summer.