You enter your spa's volume in gallons, current and target bromine levels, and current and target pH. The tool multiplies the bromine gap by volume and a dosing factor (0.0048 oz per gallon per ppm) to estimate granular bromine. pH adjustment uses a similar volumetric factor. Results assume standard granular sodium bromide and dry acid or soda ash — actual dosing varies by brand concentration.
Bromine is generally preferred for hot tubs because it remains more stable at higher water temperatures (above 75°F) and produces fewer irritating byproducts. Chlorine works but breaks down faster in warm water and may require more frequent dosing.
Test at least 2–3 times per week with test strips or a liquid test kit. Check before and after each use if the spa sees heavy bather loads. Sanitizer levels and pH can shift quickly in small water volumes.
Low pH (below 7.2) corrodes metal parts and irritates skin. High pH (above 7.8) causes cloudy water and dramatically reduces bromine or chlorine effectiveness — at pH 8.0 your sanitizer works at roughly half its rated strength.
Check the owner's manual or manufacturer's website for your model. If unavailable, multiply the average length × width × depth in feet, then multiply by 7.48 to convert cubic feet to gallons.
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.