A hot tub is not a small pool. Four hundred gallons at 102°F with three people in it is a different chemical problem from 20,000 gallons at 80°F, and the products that suit one do not transfer to the other.
Two differences drive everything. Heat uses chlorine up faster: Hot Spring's manual says dichlor stays effective substantially longer at 80°F than at 101 to 104°F. And the volume is small enough that anything you add concentrates fast. That is why spas have their own chemical aisle rather than a shelf of smaller pool bottles.
Key takeaways
- Check your tub maker's sanitizer list first. Caldera lists no bromine, and Hot Spring and Caldera ban bromine tablets.
- Dichlor is on Hot Spring's, Caldera's, Sundance's and Bullfrog's lists, and Jacuzzi starts a fresh fill with it.
- Bromine keeps working better than chlorine as pH rises, but the Alliance advises against it as the main sanitizer with ozone.
- Shock weekly. Bullfrog says so, and Hot Spring requires it on tubs with its silver purifier.
- Pool trichlor tablets never go in a spa. All five makers' manuals ban them.
My picks at a glance
- 1
Spa chlorine granules
On four of the five makers' lists · Hot Spring, Caldera, Sundance and Bullfrog tubs, and starting any fresh fill
- 2
AquaDoc Non-chlorine shock
The weekly oxidizer · oxidizing waste every week, and reactivating bromide in a bromine tub
- 3
HTH Spa bromine tablets
For a tub with a bromine feeder · tubs whose maker allows bromine tablets in a feeder
- 4
AquaDoc Sodium bromide
For a two-part bromine system · starting a bromine fill, when your tablets' label or your two-part system calls for it
Start with your tub maker's list
Before anything on this page, check what your tub's maker allows. Each manual has a list, and using something off it can cost you the warranty. The five I've read don't agree:
| Chlorine | Bromine | |
|---|---|---|
| Hot Spring | Dichlor, liquid chlorine, or its salt system | A granular brominating concentrate. No tablets, and none with its silver purifier |
| Caldera | Dichlor granules, liquid chlorine, or its salt system | None listed. Compressed bromine is banned |
| Jacuzzi J-300 | Its FROG @ease system, and dichlor to start a fresh fill | None in its ranges, and see below |
| Sundance 880 | Dichlor | Tablets in its built-in feeder, or a two-part system, and see below |
| Bullfrog | Dichlor, or its FROG @ease system | Granular bromine. Tablets only with a feeder |
Jacuzzi's and Sundance's manuals carry the same safety line: "Do not use this device with bromide products." They also say not to use any product containing sodium bromide with ozone, UV or a chlorine generator. Sundance's manual pulls both ways, because its sanitizing section offers bromine tablets and a two-part bromine system, while its ClearRay UV system comes factory-installed. On a Sundance, ask your dealer before choosing bromine.
Spa chlorine granules
Best for Hot Spring, Caldera, Sundance and Bullfrog tubs, and starting any fresh fill
Sodium dichlor is the granular chlorine the spa makers name. Hot Spring, Caldera, Sundance and Bullfrog all list it, and Jacuzzi doses it to start a fresh fill. The trade is stabilizer: every dose adds cyanuric acid, and in a few hundred gallons it builds. Bullfrog caps it at 50 ppm on its @ease system, and the Spa 56 dichlor label at 100.
Strengths
- On Hot Spring's, Caldera's, Sundance's and Bullfrog's lists
- Dissolves fast and sits close to pH neutral
- Easy to dose against a small, known volume
Trade-offs
- Adds stabilizer with every dose
- Used up faster in hot water: Hot Spring says it lasts substantially longer at 80°F than at 101 to 104°F
- Combined chlorine smells pungent, Hot Spring notes, where bromamines don't
AquaDoc Non-chlorine shock
Best for oxidizing waste every week, and reactivating bromide in a bromine tub
Potassium monopersulfate is an oxidizer, not a sanitizer. Hot Spring's manual says oxidizers like it prevent the buildup of contaminants, maximize sanitizer efficiency, minimize combined chlorine and improve clarity. The Pool & Hot Tub Alliance names it as the usual oxidizer that turns spent bromide back into active bromine, and Bullfrog lists it as one of three ways to super-sanitize each week.
Strengths
- Hot Spring and Bullfrog both list it
- Turns spent bromide back into active bromine
- Adds no chlorine and no stabilizer
Trade-offs
- Not a sanitizer: it doesn't replace chlorine or bromine
- Hot Spring says it isn't compatible with its FreshWater IQ system
Starting a bromine fill
Bromine tablets do make bromine on their own. The Alliance says they dissolve and react to produce hypobromous acid, the active sanitizer. But a feeder releases them over days, and some tablet labels call for sodium bromide on a fresh fill to get a reading sooner.
Follow your tablets' label. One EPA-registered label for 1-inch brominating tablets, Clearon's, says:
- 1
Add sodium bromide first
Half an ounce per 100 gallons, before you first use the tablets and again every time you drain and refill.
- 2
Load the feeder
Three tablets per 300 gallons, in a floating feeder or a brominator on the equipment.
- 3
Adjust it to at least 2 ppm
Then top up with three tablets per 300 gallons every 5 to 7 days, or as needed to hold 2 ppm.
Other brands' labels differ, so read the one on your container. If you test with a chlorine kit, the Alliance says to multiply the reading by 2.25 for bromine.
HTH Spa bromine tablets
Best for tubs whose maker allows bromine tablets in a feeder
Bromine keeps working better than chlorine as pH climbs. At pH 8.0 the Alliance puts 83 percent of it in its active form, against 23 percent of chlorine, and combined bromine still sanitizes. But check your tub first. Sundance builds a feeder for tablets into its tubs, Bullfrog accepts them only with a feeder and frequent testing, and Hot Spring and Caldera don't allow compressed bromine at all. Start a fresh fill the way the tablets' label says.
Strengths
- Keeps working at the high pH a spa drifts to
- Low odor, the Alliance says
- Combined bromine still sanitizes, unlike combined chlorine
Trade-offs
- Banned by Hot Spring and Caldera
- The Alliance advises against bromine as the main sanitizer with ozone
- Test strips can't separate free from combined bromine, so shock on the label's schedule
AquaDoc Sodium bromide
Best for starting a bromine fill, when your tablets' label or your two-part system calls for it
Sodium bromide isn't a sanitizer on its own. It is the bromide reserve an oxidizer turns into active bromine, which is how a two-part bromine system works, and some tablet labels call for it on every new fill. Check your tub before buying it: Jacuzzi and Sundance say not to use any product containing sodium bromide with ozone, UV or a chlorine generator.
Strengths
- What a two-part bromine system is built on
- Some tablet labels call for it at every refill
Trade-offs
- Not a sanitizer until an oxidizer converts it
- Not with ozone, UV or a salt system, Jacuzzi and Sundance say
Why shock weekly
Bullfrog's manual says to super-sanitize once a week, with non-chlorine shock, dichlor or granular bromine, and more often with heavy use. Hot Spring makes a weekly shock required on tubs with its silver purifier.
Normal sanitizing doesn't remove everything bathers leave. Bullfrog says perspiration, oils and hair sprays build up and interfere with the sanitizer, and that super-sanitizing is how you remove them.
In a bromine tub the shock does a second job: it converts spent bromide back into active bromine. The Alliance describes the cycle. Bromine that has done its work becomes bromide again, and an oxidizer reactivates it. And because test strips can't separate free bromine from combined, the Alliance says the need to oxidize is easy to overlook, so shock on the label's schedule rather than waiting for a reading to tell you.
Choosing bromine or chlorine
If your tub allows both, here is what you're choosing between.
Bromine keeps working across a wider pH range, has a low odor, and still sanitizes once it has combined with waste, where combined chlorine is a slow sanitizer. The Alliance also notes a catch: if the oxidizing gets overlooked, irritating byproducts can build up, which could mean more skin irritation with bromine than with chlorine. And it's hard to switch away from. The Alliance says water that has had bromine stays a bromine system until the bromide goes, and Bullfrog says to drain and refill before moving from bromine to its @ease system.
Chlorine, in a spa, means dichlor granules, or liquid chlorine on the makers that list it. It's dosed by hand after each soak rather than fed by a feeder. The catch with dichlor is stabilizer: every dose adds cyanuric acid, and in a few hundred gallons it climbs. The hot tub chemistry guide has the limits and the ways around it.
What not to buy
The spa aisle is the staples above plus a long tail of products for specific problems.
Enzyme treatments are sold to break down body oils. None of the makers' manuals I read calls for one, and all of them call for regular shocking and a properly cleaned filter.
Clarifiers clump fine particles so the filter can catch them. Bullfrog recommends one for fine particles such as dust. Hot Spring and Caldera say not to use one with their silver and mineral systems, because it will cloud the water. Clean the filter first either way.
Branded blends at the premium end of the shelf: read the active ingredient before assuming it is something new.
Anything sold as an alternative to draining. The Alliance says dissolved solids build until the water needs replacing, and Hot Spring says no chemical you add will oxidize soap. Only a water change resets either.
The one specialty product that earns its place on hard fill water is a stain and scale inhibitor. Bullfrog says stain and scale problems are common in hot water and recommends one, and Hot Spring suggests one for water high in dissolved minerals.
What else belongs in the cupboard
Beyond the staples above, a short list covers a spa:
- pH and alkalinity adjusters. Hot Spring's are sodium bisulfate to lower and sodium carbonate to raise. The sodium bicarbonate and sodium carbonate from a pool shed work at spa doses, and alkalinity comes first.
- Test strips. Before every soak, which is Bullfrog's rule, and at least weekly, which is Hot Spring's.
- Filter cleaner. Hot Spring and Caldera say to use a degreaser at every cleaning, because a rinse doesn't remove oil.
- Defoamer, occasionally. Hot Spring says it suppresses foam without removing the soap that causes it, and Bullfrog calls it a temporary fix.
The water change is part of the plan
Spa water gets replaced on a schedule: about every three months for Jacuzzi and Sundance, about four for Hot Spring, and every one to four for Bullfrog. The Alliance's test is dissolved solids 1,500 ppm above the fill water.
That changes what the chemistry is for. It's short-term management between water changes, not long-term balance. Draining and refilling properly resets everything, and it is a normal part of ownership rather than a failure.
Go deeperSpa chemistry in fullEach maker's targets, bromine versus chlorine, and the stabilizer limits.Frequently asked questions
Is bromine or chlorine better for a hot tub?
It depends on your tub. Bromine keeps working better as pH rises: at pH 8.0 the Pool & Hot Tub Alliance puts 83 percent of it in its active form, against 23 percent of chlorine. But Caldera's list has no bromine, Hot Spring and Caldera ban bromine tablets, and the Alliance advises against bromine as the main sanitizer alongside ozone, because the two form bromate. Dichlor is the sanitizer most of the makers list.
Why is my bromine not registering in my hot tub?
On a fresh fill, check the tablets' label. Tablets do make bromine on their own, the Alliance says, but a feeder releases them over days, and some labels call for sodium bromide first. One EPA-registered label for 1-inch brominating tablets says to add half an ounce of sodium bromide per 100 gallons before first use and at every refill, then adjust the feeder to at least 2 ppm. And if you're testing with a chlorine kit, the Alliance says to multiply the reading by 2.25 for bromine.
Can I use pool chlorine tablets in a hot tub?
No. Pool tablets are trichlor, and all five spa makers' manuals we read ban it. Bullfrog says its dissolve rate, potency and very low pH can severely damage the spa surface and components, and that using it voids the warranty. Jacuzzi and Sundance say it can damage components and burn or irritate skin. Use a spa sanitizer your maker lists.
Do I need non-chlorine shock for a hot tub?
You need a weekly shock of some kind. Bullfrog lists three: non-chlorine shock, dichlor or granular bromine, more often with heavy use. Hot Spring requires a weekly shock on tubs with its silver purifier. In a bromine tub an oxidizer also turns spent bromide back into active bromine, and non-chlorine shock does that without adding chlorine.
How often should I change hot tub water?
On your maker's interval: about every three months for Jacuzzi and Sundance, about four for Hot Spring, and one to four for Bullfrog. The Pool & Hot Tub Alliance adds a test: drain once dissolved solids are 1,500 ppm above what the fill water read.
