Pool & Hot Tub Chemistry Calc

Keep your pool and hot tub water clear, safe and balanced — for free.

Pool & Hot Tub Chemistry Calc is an easy pool chemistry calculator and water test log for pool owners and spa owners. Enter your test strip or test kit results and instantly see what to add, how much, and in what order.

★ POOL & SPA DOSE CALCULATOR
Calculate amounts for liquid chlorine/bleach, cal-hypo, dichlor, trichlor, muriatic acid, dry acid, soda ash, baking soda, calcium chloride, cyanuric acid/stabilizer and pool salt. Display amounts in grams, kilograms, ounces, pounds, mL, liters or fl oz.

★ WATER TEST LOG
Log Free Chlorine, Total/Combined Chlorine, pH, Total Alkalinity, Calcium Hardness, CYA, Salt, Bromine, Borates and Temperature. Add notes and optional test-strip/water photos.

★ SAFE TO SWIM CHECK
See whether the current water is in range, needs attention or should not be used yet. Recent chemical treatments are included in the waiting-time check.

★ CSI / LSI CALCULATOR
Use Calcium Saturation Index to understand whether water is tending toward corrosion/leaching or calcium scale. A live what-if sandbox lets you see how pH, alkalinity, calcium, temperature, salt and CYA change the result.

★ POOL VOLUME CALCULATOR
Calculate rectangular, round, oval, kidney/freeform pools, shallow/deep average depth and custom known volumes, plus hot-tub presets. Gallons and liters are shown together.

★ TRENDS & HISTORY
View 7, 30 and 90 day charts for pH, free chlorine and alkalinity, with ideal bands and rule-based trend summaries. Search, edit, duplicate and manage saved tests and treatments.

★ WEEKLY MAINTENANCE & REMINDERS
Track water testing, skimmer baskets, brushing, vacuuming, filter pressure and other custom tasks. Optional local reminders help keep maintenance on schedule.

★ SALTWATER POOL & HOT TUB SUPPORT
Targets adapt to sanitizer type, surface, CYA and pool/spa mode. Saltwater generator and bromine spa workflows are supported.

★ 100% FREE • WORKS OFFLINE • NO ACCOUNT
Core chemistry and logging features run locally and do not require an account or paid API. Your pool/spa records stay on your device. US and metric units, dark mode, phone/tablet/foldable layouts and local backup/export are included.

Pool & Hot Tub Chemistry Calc is supported by ads.

Disclaimer: Calculations are estimates. Always follow product labels, use appropriate protective equipment, add chemicals separately, circulate the water and retest. This app is not a substitute for professional advice.

Recent changes:
First release of Pool & Hot Tub Chemistry Calc — a free, offline pool and spa chemistry calculator and logbook.

- Water test log: FC, pH, alkalinity, calcium, CYA, salt, bromine, temperature
- Dose calculator: what to add, how much, in what order
- Safe to Swim status and CSI/LSI balance
- Pool and hot tub volume calculator
- History, 7/30/90-day trends and maintenance

Works offline. No account. Data stays on device.

Estimates only — follow product labels.