What's the Best Sanitizer for Hot Tubs, Bromine or Chlorine?

Publish date: 2024-10-03

Hot tubs are touted for their health benefits, but want to know something scary? Your indoor or outdoor hot tub could be a breeding ground for a bunch of nasty bacteria.

The Cleveland Clinic says improperly maintained hot tubs can be perfect hosts for germs that cause norovirus, giardiasis, and (yikes!) even Legionnaires’ disease. While public hot tubs are a greater risk for germs than private ones, you should keep your home hot tub clean and safe by regularly sanitizing with chlorine or bromine.

Both indoor and outdoor hot tubs need regular sanitation. Some might do better with bromine, others with chlorine. How do you determine which sanitizer is right for you? Let’s take a look.

Chlorine vs. Bromine

Chlorine is a toxic chemical gas derived from the electrolysis of salt brine. In its diluted liquid, granular or tablet form, chlorine has a variety of industrial uses, including as a water sanitizer.

Bromine is a corrosive, volatile, pungent chemical derived from natural brine deposits and salt bodies of water, like the Dead Sea. It’s sold in granular or tablet form for use in pools and spas.

When Is Bromine the Best Hot Tub Sanitizer?

“The unique properties of bromine make it ideal for hot tubs in many scenarios,” says Alicia Toedter, education and content leader at Leslie’s Pool Supply.

Bromine costs about twice as much as chlorine. But Toedter says bromine better maintains its efficacy at higher pH levels, which are common in aerated hot tubs. Hot tubs that run at higher temperatures (between 100 and 104 degrees) also do better with bromine, since chlorine can “gas off” quickly at those temperatures. That means bromine lasts longer.

“So bromine has another clear advantage here when it comes to maintaining sanitizer levels in your hot tub,” Toedter says. “In dark, warm, wet, covered environments ideal for germ and bacteria growth, bromine is the more effective sanitizer.”

Bromine also has a few other things going for it. Toedter says when both sanitizers combine with nitrogen-based contaminants like ammonia in the water, they form new compounds. But those combined bromine compounds, called bromamines, offer greater sanitizing power than combined chlorine compounds, aka chloramines. And, she says, “Bromamine has a less potent odor than [chloramine].”

How to sanitize a hot tub with bromine

Your bromine will come in granular or tablet form. The test strips you use for checking pH, total alkalinity and other measures in your pool or hot tub probably include a marker for measuring bromine. Test the water first to see if your bromine is low, and by how much.

To add granular bromine:

Follow the manufacturer’s directions for how many scoops of bromine to add based on the volume of your hot tub.
Add the bromine directly to the circulating spa water.
Let the spa run for about 20 minutes.
Check the bromine level with the test strips to see if it’s where it should be. The test kit will probably indicate that a “good” bromine level between two and six parts per million (ppm), but pros says that close to five ppm is ideal.

To add bromine tablets:

For this, you’ll need a floating chemical dispenser.
Insert the tablets per the manufacturer’s guidelines.
Because tablets dissolve more slowly than granules, it may take a few days for the bromine to disperse and levels to rise. Test after 24 to 48 hours.

When Is Chlorine the Best Hot Tub Sanitizer?

Since bromine breaks down quickly under the sun’s UV rays, Toedter says “chlorine is the go-to choice for uncovered outdoor hot tubs exposed to sunlight.” Chlorine also acts more quickly than bromine, so it’s ideal for killing algae fast.

Another benefit: Chlorine can be protected from the sun by adding cyanuric acid, but bromine cannot.

How to sanitize a hot tub with chlorine

Chlorine for private residential pools and spas is sold in liquid, tablet or granular form.

Unless yours is a pool and spa combo, Toedter says you can’t use trichchlor tablets, a popular form of chlorine that contains cyanruic acid. That’s probably going to leave you with granular chlorine as your option.

To add granular chlorine to a hot tub:

Check the chlorine level with a test strip.
Measure the prescribed amount of granular chlorine per the manufacturer’s guidelines (or use pre-measured packets) and add directly to the circulating spa water.
Wait at least 20 minutes, then retest the chlorine levels, which should be at about three ppm.

Toedter recommends testing your hot tub water two to three times per week, or more frequently depending on use. Periodically, you should bring a sample of your hot tub water to a pool supply store for testing. Leslie’s, like many other suppliers, offers free in-store water analysis.