Dip the test strip into the water for 2 seconds, remove it, shake it once, then immediately compare each color pad with the chart on the bottle from left to right. Compare the colors in natural or bright indoor light. The reviewed target ranges are bromine 2–4 ppm or chlorine 1–3 ppm, pH 7.2–7.8, total alkalinity 80–120 ppm, and calcium hardness 150–200 ppm.

Pool and spa test strips measure similar parameters but are calibrated for different ranges. Spa strips account for smaller water volume, higher temperature, and hot-tub target ranges—for example, bromine rather than chlorine and a slightly broader acceptable pH range. Always use spa-specific strips for hot tubs.

Compare each color pad with the chart on the bottle. For any parameter outside the target range, adjust total alkalinity first, then pH, calcium hardness, and sanitizer. Make one adjustment at a time, circulate the water for the label-directed period, and retest before making the next correction. The reviewed target ranges are alkalinity 80–120 ppm, pH 7.2–7.8, calcium hardness 150–200 ppm, bromine 2–4 ppm, and chlorine 1–3 ppm.

Hot tub chemistry is highly dynamic. Small water volume, high temperature, and jet aeration cause rapid changes. A single soak can noticeably change sanitizer and pH levels; this is normal. Testing 2–3 times per week and always before use is the best way to catch imbalances before they affect bathers or equipment.

HTH spa™ Alkalinity Up raises total alkalinity in hot tub water to the recommended range of 80–120 ppm, creating a stable buffer that prevents pH from fluctuating. Stable alkalinity helps protect equipment, surfaces, and bathers.

Hot tubs experience faster water-chemistry changes than pools because of their small water volume, high temperature, and jet aeration. Aeration causes carbon dioxide to leave the water, which can raise pH and affect alkalinity. As a result, hot tub alkalinity requires more frequent testing and adjustment—at least 2–3 times per week.