pH: The Silent Killer

Part 2 of “What Every Buyer Should Know Before Buying a Hot Tub” — a 4-part series. Read Part 1: “The Saltwater Hot Tub Myth Dealers Won’t Tell You.”

Your test strip says the pH is fine this week. Next week it’s through the roof. The week after, it’s crashed. You’re adding chemicals constantly, the water never quite feels right, and your skin itches after every soak.

Welcome to the pH rollercoaster — and if you own a saltwater hot tub, you didn’t buy a ticket. It came with the cell.

What pH actually is (60-second version)

pH measures how acidic or basic your water is, on a scale of 0 to 14. Your spa wants to live between 7.2 and 7.8 — just barely on the basic side of neutral. Stray outside that band in either direction and the water starts working against you. The cruel part: it punishes you differently on each side, and salt systems push you toward both.

High pH: the scaling side

When pH climbs above 7.8, calcium in the water starts precipitating out as scale — a crusty white buildup on the heater element, inside plumbing, around jets, and on the shell. Scale insulates the heater, which then overheats itself trying to do its job. Heaters die young in high-pH water.

The water itself turns cloudy as calcium particles stay suspended — that milky look that no amount of filtering fixes, because the problem is chemistry, not dirt.

And here’s the one that matters most: high pH cripples your sanitizer. At pH 7.5, roughly half your chlorine is in its active, germ-killing form. At pH 8.0 and above, that drops to around 20 percent. Your test strip can show a “fine” chlorine reading while the water is barely sanitizing anything. You’re swimming in under-protected water that looks and tests okay.

For bathers, high pH means dry, itchy skin and that filmy feeling that never quite rinses off.

Low pH: the corrosion side

Drop below 7.2 and the water turns acidic — and acidic water is hungry. It goes after metal first: heater elements, pump seals, jet internals, stainless fittings. They dissolve slowly and relentlessly. A heater that should last years fails in months. Seals start weeping. Then the dissolved copper and iron plate back onto your shell as green and brown stains — you get to look at the evidence of the damage without understanding the cause.

Soft parts suffer too: headrests, pillows, cover undersides, and gaskets break down faster in acidic water. Chlorine goes hyper-active but burns off fast, so levels swing wildly — strong enough to bleach, then gone entirely.

For bathers, low pH is worse than high: stinging eyes, itchy irritated skin, that “something’s wrong with this water” feeling.

And the truly nasty part: low pH is invisible. High pH at least shows itself with cloudy water and visible scale. Acidic water stays crystal clear while it eats your equipment from the inside. The first symptom most owners ever notice is a dead heater or a leaking seal — and chemical damage from imbalanced water is excluded from most spa warranties. That repair comes out of your pocket.

Why salt tubs are the worst offenders

Here’s the mechanism, and it’s baked into how salt cells work. The electrolysis process that converts salt to chlorine constantly drives pH upward — it’s not a malfunction, it’s chemistry. Every hour the cell runs, pH creeps higher.

So the salt-tub owner tests, sees 8.2, and adds acid. But judging the dose is guesswork, and most people overshoot — pH crashes to 6.8 or lower, and that’s where the real killing happens. Low pH eats the heater element and dissolves pump seals while the water looks crystal clear. Nobody notices, because nobody expects the “low maintenance” system to be corroding their spa from the inside.

The cell isn’t making acid — its relentless upward push on pH forces the owner into a permanent war with acid, and in that war, overshooting into the corrosive zone isn’t the exception. It’s the routine. Up, crash, up, crash: every downswing does silent corrosion damage, every upswing scales the heater and neuters the chlorine. The owner’s reward is equipment damage in both directions — which is exactly why the warranty documents we covered in Part 1 exclude it.

A traditionally chlorinated spa drifts too, but nothing like this. The salt cell is a pH elevator with no down button, and the owner becomes the down button — by hand, with acid, forever.

And that labor has a price tag — the hidden cost of owning a salt tub. Bottle after bottle of pH decreaser, the shock you still buy weekly, the chlorine granules you keep on hand for the days the cell can’t keep up, cartridges replaced roughly every four months. The chemical shelf never went away; the salt just added a consumables treadmill on top of it — and in some systems, a $300-to-$600 replacement cell.

Your skin keeps score

Dermatologists will tell you human skin sits around pH 5.5 — slightly acidic. Soak in high-pH water (8.0+) and it strips your skin’s natural oils: dryness, itching, that tight feeling. Soak in low-pH water and you get stinging eyes, redness, and irritation, especially on sensitive skin or any small cut. People blame “the chemicals” or “the chlorine.” Half the time, it’s the pH — swinging wildly because the salt cell won’t sit still.

The fix (and its limits)

The maintenance program is unglamorous: test pH weekly, keep total alkalinity between 80 and 120 ppm (alkalinity is pH’s shock absorber — most rollercoasters are really alkalinity problems), nudge with small doses of increaser or decreaser, and re-test after any big chemical event.

That works. But notice what it doesn’t do: it doesn’t stop the swings. It just makes you faster at correcting them. As long as the salt cell keeps pushing pH up, you’re on the treadmill — testing, dosing, correcting, repeating, for the life of the spa.

Unless the sanitizing technology doesn’t shove pH around in the first place.

Part 3 of 4 — There Are Solutions. Don’t Miss Next Week’s Post.

Mr. Fireplace Patio & Spa — Florida’s largest Jacuzzi dealer, nearly 50 years in business. Our Melbourne showroom team tests water and diagnoses equipment every day. Call (321) 727-7565.