Guide
Hot Tub Water Care: Chlorine, Bromine and a Simple Weekly Routine
Hot water, small volume and several people at once. A hot tub needs closer attention than a pool.
What changed
- : First published.
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Why hot tubs are harder than pools
A hot tub might hold 300 to 500 gallons, compared with thousands in a pool. Several people in hot water add sweat, oils and other material quickly, heat speeds up chlorine loss, and jets throw water droplets into the air. CDC notes these conditions can lead to low disinfectant levels that allow germs such as Pseudomonas (the cause of "hot tub rash") and Legionella to grow. Small volume also means small errors in dosing make big swings in levels.
The numbers CDC recommends
| Item | CDC recommendation for hot tubs |
|---|---|
| Free chlorine | At least 3 ppm (talk to the operator if above 10 ppm in a public tub) |
| Bromine | 4–8 ppm |
| pH | 7.0–7.8 |
| Temperature | No higher than 104°F (40°C) |
| Cyanuric acid | Not recommended in hot tubs |
CDC recommends testing disinfectant and pH at least twice a day for tubs in use. For a home tub used a few evenings a week, testing before each use is a sensible minimum.
Chlorine or bromine
Chlorine (usually unstabilized granules or liquid in a home tub) acts fast and is inexpensive. It is more affected by high pH and heat.
Bromine is often added as tablets in a floater or feeder, or built up as a "bank" of sodium bromide that a shock oxidizer reactivates. It tends to be steadier in hot water and less sensitive to pH. CDC's range for bromine is 4–8 ppm.
Pick one system and stay with it. Adding chlorine to a bromine tub converts bromide back into bromine, which can confuse readings; switching from bromine to chlorine generally requires a drain and refill.
Stabilized chlorine and hot tubs
Dichlor granules are widely sold for spas. Every dose adds cyanuric acid, and CDC recommends not using cyanuric acid or stabilized chlorine products in hot tubs. If you use dichlor anyway, expect stabilizer to build until you drain, and drain more often.
Dosing a small volume
Use the manufacturer's stated capacity. For chlorine, the chlorine dose calculator works for any volume: in a 400-gallon tub, raising free chlorine by 3 ppm takes about 4.5 g of available chlorine, which is about 7 g of 65% cal-hypo or 1.5 fl oz of 10% liquid chlorine. Those are small amounts, so use a measuring spoon or a marked cup kept only for that chemical, and add half, wait, and retest.
A simple weekly routine
- Before each use: test sanitizer and pH. Adjust if needed and let the jets run for several minutes before anyone gets in.
- After heavy use: add sanitizer to restore the level. Many tub manuals also call for an oxidizing "shock" after use.
- Weekly: test total alkalinity; rinse the filter cartridge with a hose.
- Monthly or as your manual says: soak the filter in a cleaner made for cartridges.
- Drain and refill on the schedule your manual gives, more often with heavy use. CDC's public hot tub guidance calls for draining and replacing all or part of the water weekly to monthly depending on use and water quality.
- Keep the cover on when not in use to reduce heat and chemical loss and keep debris out.
Healthy use
CDC also advises: shower before getting in, don't swallow the water, keep children under 5 out, avoid alcohol before or during use, and talk to a healthcare provider about hot tub use during pregnancy. After a soak, remove your swimsuit and shower with soap to reduce the risk of hot tub rash.
Troubleshooting common problems
| What you see | Likely cause | What to try |
|---|---|---|
| Cloudy water | Low sanitizer, dirty filter, high pH or alkalinity | Test and correct sanitizer and pH first, then clean or replace the filter cartridge. |
| Foam on the surface | Lotions, soaps and body oils building up in old water | Shower before use; if foam returns quickly after treatment, the water is due for a drain and refill. |
| Strong chemical smell | Combined chlorine (chloramines), not too much chlorine | Test combined chlorine; an oxidizing shock per your manual helps, and so does fresh water. |
| Sanitizer disappears fast | Heavy use, high temperature, an old filter, or the cover left off | Retest after each use, keep the cover on, and clean the filter. |
| Itchy rash after use | Possible hot tub rash from low disinfectant levels | Stop using the tub, see a healthcare provider if it does not clear, and correct sanitizer and pH before the next use. |
Keeping a record
Because levels change so quickly in a hot tub, a short record is more valuable than in a pool. Note the sanitizer and pH reading before each use, what you added, and how many people used the tub. After a few weeks you will know roughly how much sanitizer each session uses, which makes dosing faster and safer. Our water log works for hot tubs too.
Common questions
Should I use chlorine or bromine in my hot tub?
Both work at the right levels. CDC lists at least 3 ppm chlorine or 4–8 ppm bromine for hot tubs. Bromine is popular because it holds up better in hot water and at higher pH; chlorine is cheaper and works faster. Do not switch back and forth without draining.
Can I use dichlor in a hot tub?
Dichlor is widely sold for spas, but it adds cyanuric acid with every dose, and CDC recommends not using cyanuric acid or stabilized chlorine in hot tubs. If you use it, the stabilizer builds up until you drain.
Sources
- CDC, What You Can Do to Stay Healthy in Hot Tubs
- CDC, Home Pool and Hot Tub Water Treatment and Testing
- CDC, Preventing Hot Tub Rash
- CDC, Operating and Managing Public Pools, Hot Tubs and Splash Pads
Checked Nov 11, 2026. Spot an error? Tell us.