The right dose depends on your tub size and how often people use it

Most hot tubs need one bromine tablet per 250 to 500 gallons of water, added to a floating dispenser or tablet feeder. A standard 400-gallon tub typically holds two to four tablets at a time. The exact number depends on three things: your tub's total volume, how many people use it daily, and your local water chemistry.

Start by finding your tub's gallon capacity — check the manual or the manufacturer's label on the shell. Then test your water with a test strip before adding tablets. If your bromine level reads below 2 parts per million (ppm), add one tablet. If it reads between 2 and 5 ppm, your current dose is working. If it reads above 5 ppm, remove a tablet or wait longer between additions.

Bromine tablets dissolve slowly, so they work best in a floating dispenser that you can adjust by opening or closing vents. A dispenser lets you control the dissolution rate without pulling tablets in and out constantly.

Key Takeaways

  • A 400-gallon hot tub typically holds two to four bromine tablets in a floating dispenser, but your tub's exact size determines the starting point.
  • Test your water with a test strip before adding tablets, and aim to keep bromine between 2 and 5 ppm for safe, comfortable soaking.
  • Tablets dissolve faster in warmer water and with more bather load, so you may need to add tablets more often during heavy use or summer months.
  • A floating dispenser with adjustable vents gives you control over how quickly tablets dissolve without having to remove them manually.

How tub size changes your tablet count

The larger your tub, the more tablets you need. A 300-gallon tub usually starts with one tablet, a 400-gallon tub with two, and a 600-gallon tub with three. If your tub is smaller than 250 gallons, start with half a tablet or break one in half and place it in the dispenser.

Check your owner's manual for the exact gallon capacity. If you cannot find it, measure the length, width, and average depth in feet, multiply them together, then multiply by 7.5 to convert cubic feet to gallons. A tub that is 6 feet long, 4 feet wide, and 2.5 feet deep holds roughly 450 gallons.

Why water testing matters before you add tablets

A test strip tells you whether you need more bromine or whether your current tablets are still working. Dip a strip into the water away from the jets, wait the time listed on the strip bottle (usually 15 to 30 seconds), and match the color to the chart on the bottle. The bromine level should fall between 2 and 5 ppm.

If the strip shows less than 2 ppm, your tablets are dissolving too fast or you have not added enough. Add one tablet and test again in 24 hours. If the strip shows more than 5 ppm, your tablets are dissolving too slowly or you added too many. Either close the vents on your floating dispenser to slow dissolution, or remove one tablet and test again the next day.

Test your water at least twice a week, and more often if your tub gets heavy use. Heavy use means more people soaking, which burns through bromine faster.

How bather load and temperature affect tablet use

A tub used by two people once a week needs fewer tablets than one used by six people every day. Each person in the water introduces sweat, oils, and bacteria that bromine must kill, so the chemical dissolves faster. If you host frequent parties or have a family that soaks daily, expect to add tablets more often or start with one extra tablet.

Warmer water also burns through bromine faster. A tub kept at 102°F dissolves tablets more quickly than one kept at 98°F. During summer months or if you raise your temperature, check your bromine level more often and be ready to add a tablet sooner than you would in cooler months.

Floating dispensers versus tablet feeders

A floating dispenser is a plastic cage that floats on the water surface. You load tablets into it, and it has adjustable vents that control how fast the tablets dissolve. This is the most common choice for home hot tubs because it is cheap, straightforward to refill, and lets you slow down dissolution if your bromine gets too high.

A tablet feeder is a device you attach to your tub's circulation system, usually near the pump. Water flows through it and dissolves tablets on a fixed schedule. Feeders are more expensive but give you more precise control and work better if you want a completely hands-off system. Some feeders have dial settings that let you adjust the dissolution rate.

For most home tubs, a floating dispenser is the practical choice. It costs $15 to $40, holds four to six tablets, and you can adjust it by hand whenever you test your water.

What happens if you add too many or too few tablets

Too few tablets leave your bromine below 2 ppm, which means bacteria and algae can grow. Your water may turn cloudy or smell bad, and you risk skin irritation or infection. If this happens, add one tablet when ready and test again in 24 hours.

Too many tablets push bromine above 5 ppm, which causes strong chemical smell, red eyes, and skin irritation. It also wastes money because the excess bromine just sits in the water. If your level is too high, remove a tablet, close the vents on your dispenser, or drain and refill a portion of your tub with fresh water. Test again the next day.

Bromine is more forgiving than chlorine — it stays active longer and does not break down as fast in sunlight — so small mistakes are usually straightforward to fix with one test and one adjustment.

Seasonal changes and storage

If you drain your tub for winter or store it, remove all tablets from the dispenser and store them in a cool, dry place in a sealed container. Bromine tablets absorb moisture and lose strength if left exposed. A sealed plastic bucket or the original tablet bucket works well.

When you refill your tub in spring, start fresh with new tablets. Old tablets that have been sitting for months may not dissolve at the right rate. If you keep your tub running year-round, you may use fewer tablets in winter because the water is cooler and fewer people typically soak.

Frequently Asked Questions

Can I use chlorine tablets instead of bromine?

No. Chlorine and bromine are different chemicals with different dissolution rates and safety profiles. Use only the type your tub manual specifies. Mixing them or switching without draining and refilling can create dangerous chemical reactions.

How long does one bromine tablet last?

One tablet typically lasts three to seven days in a 400-gallon tub with light use, depending on water temperature and bather load. Warmer water and more people using the tub will burn through tablets faster. Test your water every two to three days to know when to add the next tablet.

What if my bromine level stays too high no matter what I do?

Close the vents on your floating dispenser completely to stop dissolution, or remove the dispenser from the water for a day or two. If the level is still too high after 24 hours, drain 25 to 50 percent of your tub and refill with fresh water. This dilutes the bromine without requiring you to buy chemicals to neutralize it.

Do I need to add tablets if I use a salt system?

No. Salt systems (salt chlorine generators) produce their own chlorine or bromine from salt, so you do not add tablets. If your tub has a salt system, follow the manufacturer's instructions for salt level and generator settings instead.

Can I break a bromine tablet in half to use less?

Yes. You can break a tablet in half with a knife or let it crack naturally as it dissolves. This is useful for small tubs under 250 gallons or if your bromine level is creeping too high. Place the broken piece in your dispenser just as you would a whole tablet.