Raising bromine in 300 gallons with MPS
| Change | Grams | Ounces |
|---|---|---|
| Bromine 0 ppm → 5 ppm | 12 g | 0.42 oz |
| Bromine 2 ppm → 5 ppm | 7.2 g | 0.25 oz |
| Bromine 3 ppm → 5 ppm | 4.8 g | 0.17 oz |
| Bromine 4 ppm → 6 ppm | 4.8 g | 0.17 oz |
How much bromine for a 300 gallon hot tub
To start a 300 gallon hot tub on bromine, add 44 g (1.6 oz) of sodium bromide to the fresh water for a 30 ppm bromide reserve, then 12 g (0.42 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 (64 g) for the start-up: on a fresh reserve it would read about 27 ppm, far above the 8 ppm maximum.
Run it with your numbers
Add
1.6oz
of Sodium bromide (bromide reserve)
44 gabout 2¼ tbsp by volume
Builds a 30 ppm bromide reserve in 300 gal. Bromide is not bromine yet; the oxidizer turns it on.
- Then turn some of it into bromine: add 0.42 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 (2.2 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.
Spa Calc for iPhoneComing soon to the App StoreAbout 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 300 gallon tub
Inflatable tubs near this size include the Intex PureSpa Bubble Massage 85" round (6 person) (290 gal) and the Intex PureSpa Jet & Bubble Deluxe 86" square (6 person) (290 gal). 300 gallons is a common 4 to 6 person size. Two people soaking for 20 minutes typically use 1 to 3 ppm of chlorine; your log will show your own number after a couple of weeks.
Questions
How much bromine to start a 300 gallon hot tub?
44 g of sodium bromide for a 30 ppm reserve, then 12 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.