Salt Cell for Your Pool

A salt cell is a short length of pipe with a stack of coated titanium plates inside it. Salty water flows through, the control box puts low voltage DC across the plates, and chloride turns into chlorine on the plate surfaces. Nothing is stored, nothing is dosed, and no chlorine exists until the pump is running.

It is also the most expensive part of a salt pool. River Pools puts a well maintained cell at three to seven years and $700 to $1,100 to replace, and retail pricing at Leslie’s runs from $899 for a Hayward T-CELL-9 to $1,949 for a Jandy AquaPure 1400. This page is about which end of that window you land on.

What is actually inside the housing

Look through the cell with a flashlight and you will see a stack of flat plates held parallel, with a narrow water gap between them. That gap is the reaction chamber, and the plates are titanium, because titanium survives salt water. Bare titanium is a poor electrode, so the working surface is a thin metal oxide coating bonded onto it. The coating does the electrochemistry, and the coating is what wears out. Manufacturers do not publish the recipe or the thickness, which is one reason nobody can quote a cell a mileage rating.

That is the whole economics of cell ownership. The titanium does not degrade. The coating does, every hour the cell is energized, and anything that makes the cell run longer for the same chlorine is spending coating you cannot buy back.

How it makes chlorine

Salt in water is sodium ions and chloride ions drifting around independently. Current across the plates pulls electrons off the chloride, and the result is chlorine that dissolves into hypochlorous acid, the form that sanitizes. Hydrogen comes off the other plate as gas.

The chlorine does its work, reverts to chloride, and goes back through the cell later. Salt is not a consumable. It only leaves with water, so if you are adding bags every few weeks you have a leak. Buying and dosing salt is on pool salt, and the arithmetic is in the pool salt calculator.

Two by-products matter more than they sound.

Hydrogen bubbles raise your pH. Not chemically. Orenda’s explanation is that hydrogen gas coming off the cell aerates the water, which drives out dissolved carbon dioxide, and losing CO2 lifts pH. Either way you will add acid more often than a chlorine pool owner does, which is on salt water pool chemicals.

The cell scales itself. Orenda notes that scale forms on the cathode side, out of the high pH sodium hydroxide produced right at the plate during electrolysis. The white crust does not drift in from the pool. Your cell manufactures it, at the spot where it does the most damage, and it builds faster when pH and calcium hardness run high.

Output percentage is a timer, not a throttle

On most residential units the output setting is a duty cycle. At 50% the cell is energized roughly half the time it has flow. A higher number does not make stronger chlorine, it makes chlorine for more minutes.

Production is capacity multiplied by percentage multiplied by pump hours, and to the coating, turning the dial up and running the pump longer cost the same. When chlorine is low, the cheaper fix is usually getting cyanuric acid into range so less of it burns off in the sun. See cyanuric acid for pool and salt water pool stabilizer.

The boost button deserves a warning. Hayward’s manual describes super chlorinate as running the cell at full output for 24 hours. In The Swim says shock mode “will only raise the FC level by a few clicks - up to 5-7 ppm,” too slowly to kill algae, and that it “places a heavy demand on the salt cell, shortening its lifespan.” If you need a shock, buy a shock: salt water pool shock.

Self-cleaning means polarity reversal

Nearly every modern cell is sold as self-cleaning. The panel flips polarity on a schedule, so the plate that was growing scale becomes the plate giving off hydrogen and the deposits get pushed loose. Production drops to nothing during the changeover, which is normal.

It works, and it is not a cleaning service. Reversal only sheds what has just started to form, so it keeps a cell in reasonable water clean and loses ground in hard water at high pH. Treat it as the reason you inspect every few months rather than every few weeks. Hayward asks for a look every 3 months, or whenever you clean the filter. What to do when you find something is on how to clean salt cell, and the routine it belongs in is on salt water pool maintenance.

What the cell can tell you, and what it cannot

Here is the fact that costs owners the most money. Your salt system almost certainly has no salt sensor. It measures how easily current crosses the water between the plates and converts that conductivity into a salinity number, temperature compensated. Poolside describes most systems as estimating “salt levels using an algorithm” rather than reading salinity directly, and Orenda adds that a faulty sensor can read lower than actual, recommending you verify with a separate salinity meter.

So the display moves when any of these change, with no salt going anywhere:

• Scale on the plates, which insulates them
• Worn coating, which reduces the active surface
• Cold water, because electrolysis is harder when it is cold
• Low flow, a dirty filter, a half-closed valve, or air in the line
• The wrong cell model selected in the menu, which rescales the whole reading

Temperature limits are model specific. Hayward states that “the Aqua Rite automatically stops generating when the pool water temperatures drops below 50ºF.” Orenda says most salt cells alarm or shut off between 55 and 59°F. Both are right about different equipment, so check your manual before you believe a spring reading.

The failure pattern that follows is predictable. A dying cell under-reports salt. The owner trusts the panel and adds a bag. The number barely moves, because salt was never low, so they add another. Owners on Inyo’s guide to reducing salt describe it in their own words. One wrote: “I added to much salt to my 15000 gallon pool because I did not realize my T-cell was going bad.” Another posted the cleanest before-and-after you could ask for: “Turned on old cell for one last reading. It was 2500. Put in new cell and it said 3600.”

Same water. Same day. A 1,100 ppm difference that was entirely instrument.

Work the three questions in order, every time:

1. Is the salt actually low? Test the water yourself, not the panel. Salt levels and testing covers how.
2. Is the cell dirty or worn? Pull it and look at the plates.
3. Is the reading wrong? Check cell type in the menu, water temperature and flow.

Sizing: buy more cell than your pool needs

Cells are rated by the pool volume they can keep sanitized, and the default move is to buy the one matching your gallons. Buy 1.5 to 2 times your volume instead. That is our recommendation, not a manufacturer instruction. A cell rated exactly at your pool size runs near 100% in July to keep up. A cell rated at double makes the same chlorine at 40 or 50%, which is roughly half the energized hours per season.

The price gap is smaller than the lifespan gap. At Leslie’s the T-CELL-9 lists at $899 and the larger T-CELL-15 at $1,099. One extra season out of the bigger unit pays that back. Sizing needs real gallons, not the number the builder told you, so start at pool volume.

OEM versus aftermarket, briefly

Third-party cells that fit Hayward, Pentair and Jandy systems cost less than the branded part, and some are good. The reason not to simply buy the cheapest is that your panel reads salinity through the cell, so a cell whose conductivity differs from what the controller expects hands you a salinity number that is quietly wrong for the rest of its life. The full comparison is on salt cell replacement.

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