Pool Types · Salt
Salt-pool chemistry, written around what a salt cell actually does.
A page for owners of pools that run on a salt chlorine generator— how the cell turns dissolved salt into free chlorine, when to inspect and clean it, the difference between topping off salt and dosing the water, and a per-parameter verdict on whether to drain-and-refill or just adjust for each of the nine measured parameters. Built to be context-aware for salt pools rather than a re-skin of the generic guidance. Written the way ClearDose writes everything else: plainly, with safety flagged, and with the chemistry terms linked back to the glossary when they come up.
The Basics
How a salt cell makes chlorine.
A salt cell— sometimes called a salt chlorine generator, or SWG — is a small electrically charged chamber plumbed into the return line after the pump and filter. As pool water passes through, a low DC voltage across titanium plates converts the dissolved salt(sodium chloride) into chlorine gas in the water. That chlorine immediately becomes hypochlorous acid — the same sanitizer a chlorinated pool gets from pucks, liquid shock, or cal-hypo.
The cell runs whenever the pump runs, and free chlorine appears continuously across the day rather than arriving as a single weekly dose. Three things still need to be true for the chemistry to hold: water sitting in the saltband the cell is calibrated for, a clean plate surface that doesn't impede electrolysis, and a stabilizer band that keeps the generated chlorine from burning off in the sun.
What the cell does not do: it does not set pH, it does not manage total alkalinity, it does not soften water that's already high in calcium hardness, and it does not getCYA to come down once it has climbed. Those changes still belong to the owner, and the rest of this page walks them.
Cell Care
When to inspect & clean the salt cell.
Salt cells scale. Calcium drops out of pool water as calcium hardnessclimbs the upper end of its range and water temperatures rise, and it tends to land on the warmest surface in the loop — which is the inside of the cell, on the plates. A scaled cell produces less chlorine per hour of pump time, runs hotter, draws more current, and dies younger than a clean one.
The standard cadence is to inspect the cell visually every couple of months and clean it whenever there is visible white scale on the plates. Most pool owners end up cleaning once or twice a season; pools with hard fill water or calcium hardness sitting at the top of the range may need to clean monthly in peak summer.
Cleaning is a mild-acid wash, not a heavy-handed scrub: turn the pump and cell off, remove the cell, rinse loose debris with a hose, then soak in a roughly 4:1 water-to-muriatic solution (or a purpose-made cell-cleaning product) until the scale dissolves — usually under fifteen minutes. Never use a wire brush or a metal scraper on the plates, and always confirm the concentration on your acid jug's label rather than relying on a universal ratio.
CYA is the lever most owners miss. When CYA climbs past 80–100 ppm, scale tends to come on faster because the cell has to run harder to keep free chlorine available against locked-up stabilizer. Holding CYA inside 30 – 50 ppm is the cheapest way to slow scale buildup and extend the interval between cleanings.
What Salt Top-Up Does (and Doesn't)
Topping off salt vs. dosing the water.
A salt top-up adds salt and only salt. It brings the salt reading up into the band the cell needs to operate, and there its job is done. A salt top-up does not raise free chlorine— the cell produces free chlorine, the top-up just gives the cell something to work with. It does not change CYA, pH, total alkalinity, or calcium hardness. It does not shock the pool or knock down combined chlorine. A top-up only fixes the one reading it is intended to fix.
Dosing is the rest of pool care: muriatic acid or dry acid to pull pH down, sodium bicarbonate to bring total alkalinity up, liquid chlorine or cal-hypo to lift free chlorine, lithium hypochlorite or non-chlorine peroxide to break combined chlorine down. Each of those is a separate decision with its own dose and its own re-test; each one can be made on top of a salt top-up without affecting the top-up's effect.
The cleanest framing: a salt top-up is mechanical maintenance of the cell's feedstock. The other six parameters are separate, and they get separate decisions. A pool that has good salt and bad pH is a dosing problem sitting on top of a working generator; a pool that has good pH and bad salt is a top-up problem sitting on top of otherwise-healthy water. Treating them as one continuous problem is how pools end up over-correcting on both at once.
Drain vs. Adjust
Drain-and-refill vs. just adjusting.
The centerpiece decision on a salt pool: for each of the nine measured parameters, is the fix a dose (or a top-up, or a cell cleaning) — or is it a partial drain and a refill from a known-zero starting point? The verdict is parameter-specific, and getting it wrong in either direction costs time: drain too often and the pool spends the season out of balance; dose too often on a parameter that only fixes by dilution and the reading never moves.
What follows is one short verdict per parameter, written for a salt pool. Every parameter links back to its glossary entry for the full safe-range and dose reasoning.
Salt cells tend to drive pH upward over time, so most salt pools reach for muriatic acid (or a dry-acid product) more often than for soda ash. pH sits on top of every other reading — get it into band first, then look at everything else.
The cell produces free chlorine continuously as long as salt, CYA, and the cell itself are all in shape. If FC drops, the fix is usually a longer pump run, a higher output percentage, or a manual dose — never a drain. CYA is the variable that decides how much FC can sit in the water without burning off in the sun.
A salt chlorine generator and a bromine feeder are mutually exclusive. Bromine pools use sodium bromide plus an oxidizer to reactivate the bromamines; salt pools use salt plus electrolysis. If the pool is running on a SWG, bromine isn't part of the chemistry.
Breakpoint-shock with liquid chlorine, cal-hypo, lithium hypochlorite, or non-chlorine peroxide — never dichlor or trichlor, since both add CYA and that is the parameter salt pools struggle most with. The practical ceiling on most SWGs is fixed by controller hardware, so a true high-CC event sometimes needs a manual dose on top of whatever the cell can produce.
Aeration + a low-pH acid dose lowers TA on a salt pool the same way it does on any other; sodium bicarbonate raises it if the buffer has eroded. Unless TA has been pushed to an extreme by a long run of over-correcting, draining solves nothing here — and a salt pool rarely needs to.
This is the one parameter where a salt pool almost always ends up reaching for the drain. Trichlor tabs and dichlor shock — both common in salt pools as a manual top-up — add CYA with every dose, and CYA doesn't degrade. Once the reading crosses ~80–100 ppm, the only real fix is partial drain-and-refill or a reverse-osmosis service where one is available. Liquid chlorine and non-stabilized shock keep CYA flat and are the way to avoid getting here in the first place.
If low: dose calcium chloride. If high: drain and refill (or run the fill water through a softener). Calcium hardness is also the parameter that drives salt-cell scaling — high CH and warm water make the cell scale faster, which shortens the interval between cleanings.
If low: top up with pool-grade sodium chloride (never table salt — iodine corrodes cells). If high: partial drain-and-refill to dilute. The salt itself is what feeds the cell, so getting it right matters for chlorine production; the trade-off is that a top-up is cheap and a partial drain is more work, so the bias is to top up early and drain only when salt sits well above band.
Borax plus a corrective acid dose on top of it — borates don't need a drain because they stay dissolved and don't accumulate the way CYA does. They soften pH drift and improve the feel of the water; some salt pool owners run them by default, others never bother. Either position is defensible.
Reading the Grid
Reading the grid.
Most parameters on a salt pool are adjustments and stay adjustments for the life of the pool. pH, free chlorine, combined chlorine, total alkalinity, and borates all move under standard dosing, and the cell itself handles most of the day-to-day chlorine production once CYA, calcium hardness, and salt read in band.
The two parameters that move a salt pool toward a drain are CYA when it climbs and calcium hardnesswhen it climbs — because neither chemical has a degradation path back down inside a filled pool. Reverse osmosis can pull either down without a drain where the service is available and the budget tolerates it; otherwise a partial drain-and-refill is the move.
The simplest rule that holds for most salt pools across most seasons: hold CYA in band with liquid chlorine (not trichlor, not dichlor), treat calcium hardness as a fill-water problem rather than a pool-water problem, and reserve draining for the two parameters that genuinely need it. Everything else is a dose.
What to check next
Walk your readings, then decide per parameter.
Take what you've got — pH, free chlorine, salt, CYA, calcium hardness — and put it through the action plan. The plan tells you the order, the size of the dose, and which numbers should defer to your product label.