Guides / Inflatable hot tub chlorine calculator
Inflatable hot tub chlorine calculator
Inflatable and small hot tubs hold only 600 to 1,200 liters, so a few grams of chlorine make a big difference. Pick your tub size and product, enter your test result, and get the dose in grams.
Formula: grams = ppm x liters / 1,000 / (strength / 100). Chlorine granules (dichlor) also add stabilizer: about 0.9 mg/l of CYA for every 1 mg/l of chlorine, so CYA builds up between water changes. Add with the jets running and the lid off, never into a bather. Everything runs in your browser.
Typical targets for a small hot tub
| Test | Aim for |
|---|---|
| Free chlorine | 3 to 5 mg/l (ppm) |
| pH | 7.2 to 7.6 |
| Total alkalinity | 80 to 120 mg/l |
| Stabilizer (CYA) | under about 50 mg/l; drain and refill when it climbs higher |
Example: a 900 liter tub at 1 mg/l that you want at 4 mg/l needs 3 x 900 / 1,000 / 0.56 = 4.8 g of chlorine granules, about one level teaspoon (scoops vary, weigh it once to learn yours).
Cloudy or foamy water?
- Cloudy: usually low chlorine, high pH or alkalinity, or a dirty filter cartridge. Test first, fix chlorine and pH, rinse the filter.
- Foam: often detergent left in swimwear, lotions or a worn-out water. Rinse swimwear in plain water; if foam keeps coming back, it is time to drain.
- Water change: small tubs build up dissolved solids and stabilizer fast. Many owners drain every one to three months.
Related: Pool chlorine calculator and what order to add chemicals in.
Want a step-by-step plan from your own test?
Clearly turns your pool or hot tub water test into an ordered plan: what to add, how much and in what order, for any brand of chemicals. It works offline and needs no account.
Clearly by Pulad Labs (Istanbul). Android, available on Google Play.
General information, not professional advice. Always follow the product label and your pool manufacturer's guidance. Never mix chemicals, add chemical to water (not water to chemical), wear eye and skin protection, and keep children and pets away while treating the water.
Frequently asked questions
How much chlorine do I put in an inflatable hot tub?
Grams = ppm to raise x liters / 1,000 / (strength / 100). For a 900 liter tub with 56 percent chlorine granules, raising free chlorine by 3 mg/l takes about 4.8 g.
What chlorine level should a hot tub have?
Free chlorine of about 3 to 5 mg/l (ppm), with pH between 7.2 and 7.6.
Why is my hot tub water cloudy or foamy?
Cloudy water usually means low chlorine, high pH or alkalinity, or a dirty filter. Foam usually comes from detergent in swimwear, lotions or old water that needs changing.
Do chlorine granules add stabilizer?
Yes. Sodium dichlor adds about 0.9 mg/l of cyanuric acid for every 1 mg/l of chlorine, so stabilizer builds up until you change the water.