What to add, in this order
Add one product at a time with the jets on and the cover open. Wait 20 minutes between products and retest.
Hot tub vs pool chemistry
A hot tub holds about 1% of the water of a pool, but it is hotter and used by the same number of people. Sweat, body oils and lotions build up fast, and germs grow faster in warm water. That is why hot tubs need a higher sanitizer level: at least 3 ppm of free chlorine according to the CDC (3–5 ppm is a good range), or 4–6 ppm of bromine.
Small volume also means small doses. A few ounces too much acid can push pH below 7 in a 400-gallon spa. Measure carefully and add a bit less than calculated if you are unsure.
Chlorine or bromine?
Chlorine (usually dichlor granules) works fast and is easy to test, but dichlor adds stabilizer every time; after a few months it builds up, which is one reason to drain regularly. Bromine is more stable at high temperatures and has less odor, but it is harder to lower once it is high and cannot be stabilized against sunlight. Both work well with a good routine.
A simple routine
- After every use: add a small dose of chlorine or non-chlorine shock.
- 2–3 times a week: test sanitizer and pH.
- Weekly: test alkalinity, rinse the filter.
- Every 3–4 months: drain, clean and refill.
Read the full hot tub water care guide.
Safety first: Always read the product label. Add chemicals to water, never water to chemicals. Add one chemical at a time with the pump running, never mix products (especially chlorine and acid), and keep everyone out of the water until levels are back in range. Wear gloves and eye protection when handling acid or shock.
Sources and methodology
Last reviewed: November 2026. Doses are calculated from the chemistry of each product (molecular weights and available chlorine) and cross-checked against manufacturer and industry dosing charts. Recommended ranges follow CDC guidance for home pools and hot tubs.
Frequently asked questions
How much chlorine should a hot tub have?
At least 3 ppm of free chlorine, and 3–5 ppm is a good working range. If you use bromine, keep 4–6 ppm.
How many gallons is my hot tub?
Most hot tubs hold 300–500 gallons. Check the manual or the manufacturer's website for your model: it is the most accurate number.
Should I use stabilizer in a hot tub?
No. The CDC recommends against cyanuric acid in hot tubs. Use unstabilized chlorine or bromine; dichlor adds some stabilizer, so drain and refill regularly.
How often should I drain my hot tub?
Typically every 3–4 months, or sooner with heavy use. A common rule is gallons ÷ 3 ÷ daily users = days between drains.