How many grams do you add?
Test alkalinity, then pH, then chlorine. The grams below come from Lay-Z-Spa’s ClearWater guides, or from the formula weight of pure bicarbonate. Your bottle wins if it prints a different dose.
Read the disclaimer before you add anything.
Test in this order
| Alkalinity | 80–120 ppm |
|---|---|
| pH | 7.2–7.6 |
| Chlorine | 3–5 ppm |
Example, before you type your own numbers
Add 36 g now.
The rest of the gap is about 18 g. Do not add that until you have tested again.
This uses the ClearWater alkalinity-increaser guide: 18 g per 1,000 litres for each 10 ppm.
Leave at least 2 hours between alkalinity, pH, and chlorine. Do not mix the powders.
Run the pump, wait at least 2 hours, and test again before a second addition.
If the grams on your own bottle differ, follow the bottle.
The ClearWater figures are for ClearWater products. Another brand can need a different weight.
Before you tip it in
- Wear gloves. Add the powder to a jug of spa water, then pour that into the spa. Do not mix two products in the same jug.
- Run the pump so the dose spreads. Keep undissolved granules away from the heater inlet.
- Wait at least 2 hours and test again. After a shock dose, wait 24 hours.
Where the numbers come from
- Lay-Z-Spa hot tub chemicals guide
Lay-Z-Spa · 2026-10-30
- Lay-Z-Spa pH Plus and pH Minus dosage guide
Lay-Z-Spa · 2026-10-30
- Lay-Z-Spa chlorine dosage guide
Lay-Z-Spa · 2026-10-30
- What you can do to stay healthy in hot tubs
CDC · 2026-10-30
- Home pool and hot tub water treatment and testing
CDC · 2026-10-30
- Sodium bicarbonate
PubChem · 2026-10-30
Questions
Why can the calculator and my bottle disagree?
ClearWater publishes 18 g per 1,000 litres for each 10 ppm of alkalinity, 10 g per 1,000 litres for each 0.1 of pH, and 9 g or 20 g per 1,000 litres of chlorine granules. Another brand prints its own weight. Use the bottle you actually have.
Is baking soda the same as alkalinity increaser?
ClearWater alkalinity increaser and pure sodium bicarbonate are the same chemical family. Baking soda is sodium bicarbonate. Washing soda is sodium carbonate and is not a substitute. The bicarbonate figure here is the formula weight, about 16.8 g per 1,000 litres per 10 ppm, close to ClearWater’s 18 g.
The chlorine reading is already high. What now?
Above 5 ppm, Lay-Z-Spa says not to use the spa. Do not add a cancelling chemical. Dilute with fresh water and test again. CDC also says not to soak when chlorine is above 10 ppm.