Pool Salt Calculator

"Saltwater pool" suggests an alternative to chlorine, and it is not one. A salt chlorine generator is a chlorine delivery system that manufactures its chlorine on site instead of having it delivered in a jug.

The cell passes a current through the water, electrolysing dissolved chloride into chlorine gas, which immediately dissolves as hypochlorous acid — the identical sanitiser produced by liquid chlorine, tablets or granules. Once it has done its work it reverts to chloride and waits to go round again.

That has three consequences worth being clear about. Everything true of chlorine chemistry is true here: the same cyanuric acid relationship, the same pH range, the same free chlorine targets, the same tests. Salt pools are not chemical-free — they need acid regularly, stabiliser, and periodic attention to calcium and alkalinity. And a salt pool with a broken cell is an unsanitised pool, which needs liquid chlorine until the cell is replaced.

What is genuinely different is the experience. Chlorine produced continuously at low concentration tends to leave lower combined chlorine than intermittent dosing does, and combined chlorine — chloramine — is what produces the smell and the eye irritation people associate with "too much chlorine". A salt pool feels softer largely because it has less chloramine, not because of the salt.

This is the most consequential fact about running a salt pool and the one most often got wrong, because the chlorinator display encourages exactly the wrong conclusion.

The chloride-to-chlorine-to-chloride cycle is closed. Chlorination consumes no salt at all. The level can only fall when salt leaves with water — splash-out, backwashing a sand or DE filter, rain overflowing the pool, a leak, or a deliberate drain.

So a salt reading that falls steadily is information. A pool losing an inch a week to a leak is losing salt in proportion, and adding salt treats a symptom while the leak keeps going. Backwashing weekly on a sand filter removes a meaningful volume over a season. Heavy splash-out from an active pool does the same.

The failure mode this creates is over-salting. Cells lose output as they age — they are consumables with a three-to-seven-year life — and many chlorinators infer salt from cell conductivity, so a worn cell reads low even when the salt is correct. The owner adds salt, the display still reads low, and more goes in. Eventually the pool sits well above the cell’s range, at which point most units fault out and stop producing entirely.

The defence is a two-dollar test strip a couple of times a season. If the strip says the salt is fine and the display says it is low, the cell is the problem.

Salt pools have a well-earned reputation for needing acid constantly, and the reason is mechanical rather than chemical.

The cell produces hydrogen gas alongside the chlorine, and the resulting turbulence at the cell surface — combined with the gas bubbles rising through the water — drives dissolved carbon dioxide out. Losing carbon dioxide raises pH. It is the same effect as running a waterfall, applied continuously whenever the chlorinator is on.

The instinct is to add acid, which works for a few days and then needs repeating. The better fix is to reduce total alkalinity, because alkalinity is the reservoir of dissolved carbon dioxide that is being driven off. A pool at 120 ppm has far more to lose, and pushes pH up far faster, than one at 70.

Salt pools are therefore run at lower alkalinity than the traditional advice suggests — 70 to 80 ppm rather than 100 to 120. Getting there uses the acid-and-aeration technique, and once it is done the acid demand falls dramatically. Many owners who arrive at a salt pool expecting it to be low-maintenance and find it needs weekly acid are running it at pool-store alkalinity.

Higher cyanuric acid is the other adjustment. A cell produces chlorine continuously at low output, and 60 to 80 ppm of stabiliser protects it better than the 30 to 50 a conventionally dosed pool wants.

At 3,200 ppm pool water is roughly a tenth as salty as seawater and about a third the salinity of a tear, which is why it tastes at most faintly saline and does not sting.

That is not nothing, though, and salt does accelerate corrosion of some materials. The vulnerable items are consistent: ladders and handrails, especially where a stainless fitting meets a wet concrete deck; light rings; heater headers and any exposed copper; and natural stone coping, where salt crystallising in the pores can spall the surface over years.

The mitigations are mostly about water management rather than the salt level. Rinse coping and decking after heavy splash-out, keep the water chemistry balanced so the water is not aggressive on top of being salty, and ensure any sacrificial anode fitted to the system is in place and not exhausted. Bonding — the electrical connection between metal components and the pool structure — matters more in a salt pool than a conventional one, and a corrosion problem that appears suddenly is worth having the bonding checked for.

Cells themselves scale rather than corrode. Calcium carbonate builds on the plates, particularly on a pool running a positive saturation index, and it insulates them. Most cells self-clean by reversing polarity, which handles a normal rate of deposition; a scaled cell that needs acid washing usually means the saturation index has been positive for a while, and correcting that is the real repair.