Hot tub water chemistry: ideal levels chart

The ideal hot tub levels are pH 7.2–7.8, total alkalinity 80–120 ppm, free chlorine 1–3 ppm (or bromine 3–5 ppm), and calcium hardness 150–250 ppm. Keep those four in range and most water problems never start.

Ideal levels chart

Reading	Ideal range	Too low causes	Too high causes
pH	7.2–7.8	Stinging eyes, corrosion of heater and seals	Scale, cloudy water, weak sanitizer
Total alkalinity	80–120 ppm	pH swings, corrosion	pH that will not come down, scale, cloudiness
Free chlorine	1–3 ppm	Bacteria, cloudy or green water	Skin and eye irritation, faded swimwear
Bromine	3–5 ppm	Bacteria, cloudy water	Irritation, strong odor
Calcium hardness	150–250 ppm	Foam, corrosion	Scale on heater and shell, cloudy water
Cyanuric acid (dichlor users)	About 30–50 ppm	Not a concern in a covered tub	Chlorine stops working well. Drain and refill.
Water temperature	100–102°F typical, 104°F maximum	Comfort only	Overheating risk for bathers

A note on sanitizer: 1–3 ppm chlorine and 3–5 ppm bromine are the ranges on most residential spa product labels. The CDC recommends at least 3 ppm free chlorine or 4–8 ppm bromine in hot tubs, so aim for the top of the range, especially with several bathers.

The order to balance in

1. Total alkalinity. It anchors pH. Raise it with alkalinity increaser, lower it with pH decreaser. See the alkalinity guide.
2. pH. Adjust with pH increaser or decreaser. See pH too high or too low.
3. Calcium hardness. Check after every refill. See the calcium hardness guide.
4. Sanitizer. Add chlorine or bromine once pH is in range.
5. Shock. Weekly, or after heavy use.

Add one product at a time with the jets running. Wait 20 to 30 minutes and retest before the next one. Follow each product label for the dose for your tub's volume, and never mix chemicals.

What each number really does

pH

pH is a 0 to 14 scale of acid to base. Your eyes are about 7.4, which is why the middle of the range feels best. pH also controls how hard chlorine works. At pH 7.2 most of your free chlorine is in its active form. At pH 8.0 only about a fifth of it is. That is why a tub can test fine for chlorine and still turn cloudy when pH is high.

Total alkalinity

Alkalinity is the water's resistance to pH change. Under 80 ppm, pH jumps around with every bather and every dose. Over 120 ppm, pH drifts high and resists coming down.

Sanitizer

Free chlorine is the chlorine still able to kill germs. Total chlorine includes the used-up portion, called combined chlorine or chloramines. If total is more than about 0.5 ppm above free, the tub needs a shock. Bromine works a little differently: used bromine can be reactivated by shock, which is part of why it lasts well in hot water.

Calcium hardness

Water wants some calcium. With too little, it pulls minerals from metal parts and foams easily. With too much, calcium drops out as rough white scale, starting in the hottest place, which is the heater.

Total dissolved solids

Everything you add stays in the water as dissolved solids. When the water is 3 to 4 months old, it gets harder to balance and looks flat. That is the signal to change the water, not to add more product.

Quick diagnosis by symptom

Symptom	Check first
Cloudy water	Sanitizer low, pH high, dirty filter
Strong chlorine smell	Combined chlorine. Shock the tub.
Itchy skin or red eyes	pH out of range or sanitizer too high or too low
Foam	Soft water, soaps and lotions, old water
White flakes or rough shell	High calcium and high pH
Green tint	Low sanitizer (algae) or metals in the fill water

How often to test

Test 2 to 3 times a week and before any heavy-use evening. Strips are fine for routine checks. If reading the colors is a chore, see how to read test strips or snap a photo and let the AskTub strip reader give you the numbers and the next step.