How much bromine for a 500 gallon hot tub

To start a 500 gallon hot tub on bromine, add 74 g (2.6 oz) of sodium bromide to the fresh water for a 30 ppm bromide reserve, then 20 g (0.71 oz) of 45% MPS to turn some of it into bromine: after 15 minutes with the jets on it should read about 5 ppm. After that, bromine tablets in a floater and shock after soaks keep it at 4 to 6 ppm.

Don’t use the full label shock (106 g) for the start-up: on a fresh reserve it would read about 27 ppm, far above the 8 ppm maximum.

Raising bromine in 500 gallons with MPS

With a bromide reserve in place. Non-chlorine shock, 45% MPS. The first row is the fresh-fill start-up.
Change	Grams	Ounces
Bromine 0 ppm → 5 ppm	20 g	0.71 oz
Bromine 2 ppm → 5 ppm	12 g	0.42 oz
Bromine 3 ppm → 5 ppm	8 g	0.28 oz
Bromine 4 ppm → 6 ppm	8 g	0.28 oz

Run it with your numbers

Add

2.6oz

of Sodium bromide (bromide reserve)

74 gabout 3¾ tbsp by volume

Builds a 30 ppm bromide reserve in 500 gal. Bromide is not bromine yet; the oxidizer turns it on.

Then turn some of it into bromine: add 0.71 oz of Non-chlorine shock (MPS 45%) with the jets running. After 15 minutes bromine should read about 5 ppm. Test before anyone soaks.
Don't use a full shock dose (3.8 oz) for this: on a fresh bromide reserve it would read about 27 ppm, far above the 8 ppm maximum.
After that, keep bromine tablets in a floating feeder and shock after soaks. You only rebuild the reserve after a drain and refill.

Check the product label. Strengths vary by brand, so enter the % printed on yours. Add one chemical at a time, into the water, and never mix chemicals.

Save this test and get a reminder before your next soak.

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About bromine

Bromine tablets alone dissolve slowly and take days to bring a fresh tub up to range, which is why the sodium bromide reserve comes first. You add it once per fill. Each oxidizer dose (MPS or chlorine) turns spent bromide back into active bromine.

Test kits read bromine on the chlorine scale × 2.25. If your kit gives chlorine only, multiply by 2.25. Use the converter.

Don’t switch between bromine and chlorine without draining: once there is bromide in the water, chlorine just makes more bromine.

A 500 gallon tub

500 gallons is a typical 6 to 7 person acrylic tub. Doses are larger but the water is steadier; still test before every soak, and drain about every 83 days with two soakers a day.

Questions

How much bromine to start a 500 gallon hot tub?

74 g of sodium bromide for a 30 ppm reserve, then 20 g of 45% MPS to bring bromine to about 5 ppm.

How many bromine tablets do I need?

Tablets go in a floating dispenser; set the floater so bromine holds at 4 to 6 ppm between soaks and adjust after testing. The number of tablets depends on your floater and use.

How long after adding bromine can I soak?

Wait about 15 minutes with the jets running, then test. Soak when free chlorine is 3 to 5 ppm and at least 7.5% of your CYA (bromine 4 to 6) and pH is 7.2 to 7.8, at least 15 minutes after adding anything (20 after pH decreaser); after chlorine, bromine or a shock, test again first. Above 5 ppm chlorine or 6 ppm bromine, wait and retest in an hour or two; never soak above 10 ppm chlorine or 8 ppm bromine, or with pH below 7.0 or above 7.8. Below 3 ppm chlorine (4 bromine), add sanitizer first; at pH 7.0 to 7.2, raise pH first; with CYA above 40 ppm, drain and refill. Hot tub limits based on CDC guidance and EPA product labels.