How a Pool Chlorinator Works, and the Three Types

A pool chlorinator is a device that doses chlorine into the water so you do not have to pour it in by hand. Most types hold solid chlorine, tablets in a plumbed canister or in a floating dispenser, and release it as water flows past or as the tablet dissolves. A salt chlorinator works the other way around: it holds no chlorine at all and makes it on site from salt already dissolved in the pool. Leslie’s describes that step accurately: when the salty pool water passes through the chlorine generator cell, a low voltage electrical charge zaps the salt particles and transforms them into hypochlorous acid, which is chlorine.

Do salt pools have chlorine, and do salt pools use chlorine

Yes, to both. They are the same question and the answer is that a salt pool is a chlorine pool that manufactures its own supply instead of buying it in a bucket. The sanitizer doing the work in a salt pool is the same hypochlorous acid doing the work in a tablet pool. What changes is where it comes from and what else arrives with it, which is the whole point of the comparison below.

The three types of pool chlorinator

Leslie’s sets out all three. An automatic chlorinator asks you to calculate your pool’s volume, fill the canister with tablets, and set the dial to your desired chlorine level, and because it sits after the filter it chlorinates downstream of your equipment. The catch is plumbing: an in-line model needs enough straight return line to fit in. If you do not know your volume, the pool volume calculator settles it before you set any dial.

A salt chlorinator is the most automatic of the three and can run for months without intervention, with salt only needing replenishment when it is lost to backwashing, splashing or draining. The costs are the honest downside: upfront price, cell replacement every 3 to 7 years, and converting the water in the first place. Those numbers are laid out on the cost to install a salt water pool page.

Floating chlorinators are $10 to $45 and they are cheap for a reason. Leslie’s lists spillage causing chlorine spikes, the float getting trapped against a surface and staining it, and a safety concern around children.

What each type puts in your water besides chlorine

This section is our analysis, built from the sources linked in it. The comparison above is how the three types are usually presented, on convenience and price, and that comparison is silent on chemistry. Leslie’s article makes no claim about cyanuric acid, calcium or pH for any of the three, so none of what follows is attributed to it. It matters anyway, because the thing your chlorinator adds alongside chlorine is what you will be living with in five years.

The numbers for dichlor and cal-hypo come from Leslie’s shock comparison, which states that dichlor is 55% available chlorine and contains cyanuric acid, which will increase residual CYA in the pool over time, and that cal-hypo is 70% available chlorine, does not contain cyanuric acid, adds calcium, and has a pH of 10.8 to 11.8. Our sources publish those figures for dichlor rather than for trichlor, but the mechanism is the same one: a stabilized chlorine carries its stabilizer in with it. That is what the 3 inch tablets in a feeder canister are. If you want the chlorine without the stabilizer, that is the subject of chlorine tablets without cya.

A salt cell makes unstabilized chlorine, which is why it adds no cyanuric acid and no calcium. Cal-hypo is also unstabilized, and it carries calcium instead. If the word itself is doing work you cannot see, read unstabilized chlorine for pools.

Inline vs offline tablet feeders

The tablet feeder above comes in two plumbing styles. An inline feeder is a canister spliced into the return pipe, so the whole return flow runs over the tablets. One manufacturer’s instructions place it in the return line between the pool and any other components of the circulation system, including heater, filter and pump, vertical, lid up.

An offline, or off-line, feeder sits beside the equipment instead, fed by a small bypass. One Pentair guide offers it for where permanent installation into the return line is impractical: most above ground pools, and any pad with no spare straight pipe. Hayward’s off-line feeder manual has you drill the existing pipe and clamp on saddle fittings, taking the inlet after the pump and before the filter and the outlet after the heater. If no heater is being used, connection should be made after the filter.

That outlet is where the check valve goes, and it is not optional. Hayward’s instruction is that an in-line positive seal corrosion resistant check valve should be installed to reduce backflow of chlorine gas when the system is shut off. Skip it, and when the pump stops, a canister of concentrated, acidic tablet solution and chlorine gas drains backward into your equipment. Pentair says the valve will prevent the backflow of corrosive liquids and gases and warns that a mixture of air and chlorine is highly corrosive to metals. Hayward is blunter: damage to the heater or filter may result if concentrated chlorine is allowed to flow through them.

Both styles meter the dose with a dial, not a measurement. Hayward’s is a flow control valve you set by results: check chlorine residual daily and adjust the dial valve for more or less chlorine.

Neither style changes what is in the tablet. Trichlor carries its own stabilizer, and the industry association’s fact sheet gives the ratio: 0.6 ppm of cyanuric acid is added to the water for each ppm of available chlorine added. Orenda measures it by weight: one pound of trichlor in 10,000 gallons of water increases the CYA level by 6 to 6.5 ppm. The same sheet notes that pH and alkalinity of treated water may drift down with trichlor in use.

Which is why a salt pool owner rarely wants either feeder running full time. The cell already makes chlorine and adds no stabilizer. A feeder left open alongside it raises the number that sets your free chlorine floor, and as the section above says, that number only comes down by replacing water. Keep one for a vacation week, then close the dial. See best range of cya for a salt pool and the cya chlorine chart.

Why the cyanuric acid number decides your chlorine target

Cyanuric acid is not a contaminant. It shields chlorine from sunlight. The cost is that it also holds chlorine back, so the more of it you accumulate, the higher the free chlorine floor you have to maintain to get the same sanitizing effect. Trouble Free Pool puts the minimum free chlorine for a salt pool at about CYA x 5%, against about 7.5% for a manually chlorinated pool, and the same relationship is available as a table with a salt pool column.

Run the multiplication. At 70 ppm cyanuric acid, a salt pool’s floor is 70 x 0.05 = 3.5 ppm free chlorine, held continuously. At 40 ppm it is 40 x 0.05 = 2 ppm. Same pool, same water, nearly double the chlorine demand, purely because of a number that arrived with the tablets. For reference, Hayward’s AquaRite manual targets stabilizer at 30 to 50 ppm.

Now the part that makes a tablet feeder a long term commitment rather than a convenience. Cyanuric acid does not leave. Orenda is direct about it: only draining and diluting, or reverse osmosis, actually reduce CYA. It does not burn off, and no additive removes it. So a chlorinator full of trichlor tablets is quietly raising a number you can only lower by replacing water. Nothing in the convenience comparison tells you that.

What a salt cell adds that the other two do not

Being fair goes both ways. A salt cell has two side effects of its own and they are not optional.

The first is pH. Electrolysis off-gasses hydrogen, that aeration drives carbon dioxide out of the water, and driving off CO2 raises pH. That is the real reason salt pools drift upward in pH, not the chlorine itself. Expect to add acid on a schedule, and see how to lower pH in a salt water pool.

The second is scale. During electrolysis, scale forms on the cathode side of the plates where local pH is high, and polarity reversal fractures it off into the pool as white flakes that test as calcium carbonate. Orenda’s response is to run alkalinity at 60 to 70 ppm for salt pools and cell output at 40 to 80%.

Worth knowing while you are choosing: a salt system has no salt sensor. It measures how easily current crosses the cell and infers salinity from that, temperature compensated, so cold water makes the display read low while the salt has not moved. Scale, plate wear and low flow do the same thing. That is worth understanding before you own one, and it starts with what the salt cell for pool page covers, along with the rest of our salt cell coverage.

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