Every bromine owner eventually asks the same question: how much do I actually add? The target range — 3 to 5 ppm free bromine — is printed on every product label, but no label tells you whether that means one tablet or four, or how many ounces of sodium bromide go into a 400-gallon tub at first fill.
This guide gives you concrete numbers for both bromine systems (tablets and granules), sized by hot tub volume and adjusted for bather load.
Two systems, two dosing approaches
Bromine hot tubs run on one of two chemistry systems:
Tablet system — 1-inch BCDMH tablets in a floating dispenser or inline feeder dissolve slowly and release active bromine continuously. You manage dose by how many tablets are in the floater and how far the vents are open. No separate activation step is needed.
Granule system — You maintain a reservoir of inactive bromide ions in the water (the "bromide bank") using sodium bromide granules, then convert those ions into active bromine by adding an oxidizer (typically MPS non-chlorine shock) after each soak. The two products work together; neither sanitizes on its own.
The dosing math is completely different for each system. Know which one you're running before reading the tables below.
Target range: 3–5 ppm free bromine. Below 2 ppm, bacteria can establish. Above 8 ppm, the water is irritating and wastes chemical. Test at least twice a week — more often in hot weather or after heavy use.
Tablet system dosing
Starting out
Load your floating dispenser with the first batch of tablets and drop it in the hot tub the day of the fill. The floater will take 12–24 hours to establish a baseline bromine level. Test after 24 hours and adjust the vent setting:
- Level below 2 ppm: Open vents fully or add tablets. Let run another 12 hours and retest.
- Level 3–5 ppm: Good. Note vent position as your baseline for this season.
- Level above 6 ppm: Partially close vents. Lift the cover for 30 minutes to off-gas.
Unlike chlorine, you do not establish a bromide bank with the tablet system — the tablets release both the bromide and the oxidizer in one compound. This makes startup simpler but correction slower (tablets dissolve over days, not hours).
Tablets per week by tub size
These ranges assume standard 1-inch BCDMH spa tabs (20-gram tablets). "Sessions" means the number of times the tub is used in a given week.
| Tub size | 1–2 sessions/week | 3–4 sessions/week | Daily or 3+ bathers |
|---|---|---|---|
| 200–300 gal | 1–2 tablets | 2–3 tablets | 3–4 tablets |
| 300–400 gal | 2–3 tablets | 3–4 tablets | 4–5 tablets |
| 400–500 gal | 3–4 tablets | 4–5 tablets | 5–7 tablets |
| 500–600 gal | 4–5 tablets | 5–7 tablets | 7–8 tablets |
A single 1-inch tablet dissolves in roughly 5–7 days in a 300–400 gallon tub with the floater vent halfway open. Hotter water and wider-open vents speed dissolution. The table above reflects weekly consumption at roughly that rate.
Adjust based on test results, not just the table. If your 400-gallon tub is reading 2 ppm mid-week with 3 tablets in the floater, open the vent wider or add a fourth tablet next refill. If it reads 7 ppm, close the vent or let the floater empty before reloading.
Floater vent management
Most floating dispensers have adjustable vents that control how much water flows through the dissolving tablets:
- Fully open: Maximum dissolution — good for hot weather, high bather load, or correcting low levels
- Half open: Typical baseline for moderate use (2–4 sessions/week, 75–85°F water)
- Mostly closed: Slow dissolution — useful in cool seasons or when usage drops off
Don't leave the floater directly against the shell or jets. It bleaches acrylic on contact. Set a floater with enough buoyancy to drift freely, or use an inline feeder on the return line.
Weekly shock for tablet users
Tablet systems need a weekly MPS oxidizer shock even when bromine levels look fine. Here's why: tablets release active bromine, but combined bromine (bromamines — the spent, irritant form) builds up over time. MPS breaks down combined bromine and reactivates the bromide ions that tablets continuously add to the water.
Skip the weekly shock and you get a tub that smells "bromey" even at 4 ppm — that's combined bromine, not a dosing problem.
Weekly MPS shock dose for tablet system:
| Tub size | MPS shock per week |
|---|---|
| 200–300 gal | 1–1.5 oz (30–45 g) |
| 300–400 gal | 1.5–2 oz (45–60 g) |
| 400–500 gal | 2–2.5 oz (60–75 g) |
| 500–600 gal | 2.5–3 oz (75–90 g) |
Add shock after soaking, not before. Dissolve in a cup of warm water first, then pour around the perimeter with the jets running. Wait 15–20 minutes before covering.
Granule system dosing
The granule system has two phases: initial fill (establishing the bromide bank) and ongoing maintenance (replenishing the bank and reactivating it after each soak).
Initial fill: building the bromide bank
This is the step most new granule-system owners get wrong. You cannot just add sodium bromide and expect sanitation — bromide ions are inert until activated by an oxidizer. But you also cannot just shock first without bromide — there's nothing to activate.
Step 1 — Add sodium bromide (establishing the bank):
| Tub size | Sodium bromide (initial fill) |
|---|---|
| 200 gal | 4 oz (about ½ cup) |
| 300 gal | 6 oz (about ¾ cup) |
| 400 gal | 8 oz (about 1 cup) |
| 500 gal | 10 oz (about 1¼ cups) |
| 600 gal | 12 oz (about 1½ cups) |
Pre-dissolve sodium bromide in a bucket of warm hot tub water before adding. Pour around the perimeter with jets running. Let circulate for 10 minutes.
Step 2 — Activate with MPS shock:
| Tub size | MPS shock (activation dose) |
|---|---|
| 200 gal | 2 oz (60 g) |
| 300 gal | 3 oz (90 g) |
| 400 gal | 4 oz (115 g) |
| 500 gal | 5 oz (140 g) |
| 600 gal | 6 oz (170 g) |
Add MPS around the perimeter with jets running. Wait 30 minutes, then test. Your bromine level should read 3–5 ppm. If it reads below 2 ppm after 30 minutes, the sodium bromide dose was insufficient — add another 2 oz per 100 gallons and shock again.
The bromide bank is now established. All future maintenance works by replenishing this bank (small sodium bromide additions monthly) and reactivating it after each soak (MPS shock after use).
After-soak maintenance (granule system)
Every soak depletes active bromine and converts it to combined bromine (bromamines). The MPS shock after each use does two things: breaks down bromamines and reactivates the bromide ions into fresh active bromine.
Post-soak MPS dose (granule system):
| Tub size | 1–2 bathers | 3–4 bathers | 5+ bathers |
|---|---|---|---|
| 200–300 gal | 1 oz | 1.5 oz | 2 oz |
| 300–400 gal | 1.5 oz | 2 oz | 2.5 oz |
| 400–500 gal | 2 oz | 2.5 oz | 3 oz |
| 500–600 gal | 2.5 oz | 3 oz | 4 oz |
Add within 30 minutes of exiting the tub. Dissolve in a bucket of warm water, pour around the perimeter with jets running. Wait 15–20 minutes before covering.
Test bromine before the next soak. If the level is still above 3 ppm before you get back in, you dosed correctly. If it reads below 2 ppm, increase your post-soak dose by 0.5 oz next time.
Monthly sodium bromide replenishment
The bromide bank slowly depletes over time even with regular shocking — some bromide is oxidized past the point of reactivation and leaves the water through evaporation and splash-out. A small monthly sodium bromide addition maintains the bank size.
Monthly replenishment (granule system):
| Tub size | Sodium bromide per month |
|---|---|
| 200–300 gal | 1–2 oz |
| 300–400 gal | 2–3 oz |
| 400–500 gal | 3–4 oz |
| 500–600 gal | 4–5 oz |
Watch for this sign that the bank is depleted: bromine levels don't rise adequately even after a full shock dose. That's the cue to add sodium bromide before the next shock, not to add more MPS.
Correction doses (when bromine is too low)
Low bromine (below 2 ppm) requires different action depending on the system.
Tablet system — low bromine:
- Test that the floater has tablets in it. An empty floater is the most common cause.
- Open the vent fully and let run for 12–24 hours.
- If level doesn't recover after 24 hours with an open, stocked floater, the water may have a high bromamine load. Shock with 2–3 oz MPS per 100 gallons (double the standard weekly dose). Let jets run 30 minutes with the cover off, then retest.
Granule system — low bromine:
- Check when you last added sodium bromide. If it's been more than 6–8 weeks, the bromide bank may be depleted.
- Add sodium bromide (1 oz per 100 gallons), let circulate 10 minutes.
- Then shock with MPS (2 oz per 100 gallons). Retest in 30 minutes.
- If the level rises to 3+ ppm within 30 minutes, the bank was depleted. Schedule monthly replenishment going forward.
- If the level stays below 2 ppm even after sodium bromide + MPS, the water may be too old. Drain and refill.
Emergency boost (either system): A small dose of dichlor chlorine granules (1 tsp per 300 gallons) works as a fast-acting bromine activator. Dichlor reacts with residual bromide ions and raises bromine level within 20–30 minutes. It adds a small amount of CYA per dose — fine for occasional emergency use, not a substitute for regular sodium bromide additions.
How temperature affects bromine demand
Bromine is more stable than chlorine at high temperatures — it's one of the reasons bromine is preferred for hot tubs over chlorine. But heat still accelerates consumption:
- 104°F (max): Bromine depletes roughly 2× as fast as at 95°F. Test before every soak and shock after every use.
- 95–100°F (typical): Standard dosing tables apply.
- Below 90°F (cool soak): Bromine demand drops. Tablet floaters can be adjusted to half-open or less; post-soak shock can be reduced by 30%.
Sunlight matters for outdoor tubs. Unlike chlorine, bromine has no cyanuric acid stabilizer equivalent. UV light degrades active bromine in outdoor tubs significantly faster than in covered indoor installations. If your tub is uncovered outdoors in direct sun, plan to test daily and increase your weekly dose by 20–30%.
Complete weekly maintenance routine
This routine applies to both tablet and granule systems.
Before every soak:
- Test bromine (target 3–5 ppm) and pH (target 7.2–7.6)
- Do not enter if bromine is below 2 ppm or above 8 ppm
- Adjust pH if outside range before adjusting bromine
After every soak:
- Add MPS shock (see post-soak table above)
- Leave cover off for 15 minutes to allow off-gassing
- Replace cover
Weekly:
- Full chemistry panel: bromine, pH, total alkalinity (80–120 ppm), calcium hardness (150–250 ppm)
- Tablet users: shock with standard MPS dose even if bromine looks fine
- Granule users: check sodium bromide bank level (if post-soak shocks aren't lifting bromine adequately)
- Rinse filter with garden hose
Monthly:
- Granule users: add sodium bromide replenishment dose
- Deep-clean filter (overnight chemical soak in filter cleaner)
- Clean waterline and cover underside
- Full chemistry test including CYA if you use dichlor as an emergency activator
Every 3–4 months:
- Drain and refill
- Before draining, run a line-flush product (Natural Chemistry Spa Purge or similar) to clear biofilm from plumbing lines
Common bromine dosing mistakes
Skipping sodium bromide at first fill (granule system). Shocking without a bromide bank gives you nothing — MPS has nothing to activate. If your granule tub never gets above 1 ppm no matter how much shock you add, this is usually the cause.
Not shocking after every soak. Bromine regenerates only when the bromide ions are reactivated. Without post-soak shocking, active bromine depletes and combined bromine (bromamines) builds up. The tub smells "chemical" even at 4 ppm.
Using the same tablet dose year-round. Summer heat and outdoor UV exposure double bromine demand. The floater setting that maintained 4 ppm in October will read 1 ppm in July. Increase dose proactively when temperatures rise.
Adding MPS immediately before soaking. MPS spike can briefly drive bromine above 8 ppm. Always shock after soaking, not before. If you need to shock before use (contamination event), wait at least 30–45 minutes with jets running and retest before entering.
Not replacing sodium bromide in the granule system. MPS shock reactivates the bromide bank but doesn't replace ions that have left the water. Monthly replenishment prevents a slowly depleting bank that eventually stops responding to shock altogether.
Testing immediately after adding chemicals. Wait at least 20–30 minutes with jets running before testing. Chemicals need to fully circulate and react before your reading is accurate.
Recommended products
| Product | Use |
|---|---|
| Leisure Time Brominating Tablets | Primary sanitizer for tablet system — 1-inch BCDMH tablets for floater or inline feeder |
| Leisure Time Sodium Bromide | Bromide bank establishment and replenishment for granule system |
| Leisure Time Renew Non-Chlorine Shock | MPS oxidizer — reactivates bromide bank after every soak and breaks down bromamines |
| Taylor K-2006 Drop Test Kit | FAS-DPD liquid test — most accurate kit for measuring free and combined bromine separately |
| AquaChek 7-in-1 Test Strips | Fast daily test strips — measures bromine, pH, alkalinity, hardness in one dip |
The Taylor K-2006 measures both free and combined bromine — this distinction matters for bromine systems because high combined bromine (bromamines above 0.5 ppm) explains the "strong chemical smell" that owners sometimes misdiagnose as a dosing problem. AquaChek strips are faster for daily routine checks.
For the granule system, buy sodium bromide and MPS shock from the same manufacturer at the start so dosing ratios are calibrated to each other. Mixing brands works but requires more trial-and-error adjustment.
Frequently asked questions
How often should I add bromine tablets? Top up the floater when it's less than half full, which is typically every 5–7 days for a 300–400 gallon tub at moderate use. Don't wait until the floater is completely empty — bromine levels drop noticeably in the last day or two before the final tablet dissolves. Check the floater every 3 days when starting out.
How much sodium bromide do I add each time? At first fill: about 2 oz per 100 gallons. Monthly replenishment: about 0.5–1 oz per 100 gallons. Only add sodium bromide when the bank seems depleted (post-soak shocks aren't raising bromine adequately) — adding too much doesn't hurt but wastes product.
Can I use bromine tablets and the granule system together? Technically yes, but there's no benefit. Tablets continuously add bromide and oxidizer in one compound; the granule system's sodium bromide just adds more bromide that the tablets will eventually oxidize anyway. Pick one system and stick to it. If you want faster correction than tablets allow, switch fully to the granule system rather than combining.
My bromine won't go above 2 ppm no matter how much I add — what's wrong? For granule-system users: the bromide bank is almost certainly depleted or was never established. Add sodium bromide (2 oz per 100 gallons) and wait 10 minutes, then shock. For tablet users: check that the floater is stocked and vents are open, then do a double-dose MPS shock. If neither fixes it, the water may be old — drain and refill and start fresh.
Is it safe to soak when bromine is at 6 ppm? Yes. The acceptable range for hot tub bromine is 2–8 ppm, and most guidelines suggest 3–6 ppm as the operating window. At 6 ppm you're at the upper end but not outside safe limits. High bromine causes eye and skin irritation at prolonged exposure. If your tub regularly sits at 6+ ppm, reduce the floater dose or extend the interval between post-soak shocks.
Can I switch from bromine to chlorine? Yes, but you need to drain first. Residual bromide ions in the water will convert any added chlorine into bromine — the tub will test as a bromine tub indefinitely. There is no chemical flush that removes bromide from water. A full drain, shell rinse, and fresh fill is the only way to switch sanitizer systems.
The two most important habits for a bromine tub: test before every soak, and shock (reactivate) after every soak. Everything else — sodium bromide replenishment, filter cleaning, quarterly drains — flows from keeping that basic rhythm consistent.
For the full chemistry picture, see the hot tub water chemistry guide for beginners and the bromine vs. chlorine complete comparison. If you're deciding between the tablet and granule form before committing to a system, the bromine tablets vs. granules guide covers the tradeoffs in detail. And when you're ready to set up a full testing and maintenance cadence, the hot tub chlorine schedule guide (the structure applies equally to bromine tubs) lays out the full routine.
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