Bromine Test Question

Aug 21, 2018
San Antonio, TX
The bromide bank does not deplete and you typically establish it using sodium bromide. When you add any source of chlorine to the water, the chlorine "activates" (oxidizes) the bromide (Br-) to bromine (Br+). When the bromine sanitizes or oxidizes something, it gets reduced back to bromide again.

The cheapest thing to activate bromide would be plain laundry bleach. You can also use dichlor powder as well. Bromine "tabs" are typically a mixture of brominated and chlorinated dimethylhydantoin (DMH) and so the chlorine is already present to "activate" the bromine. However, just like CYA can over stabilize a chlorine sanitized pool, DMH can over stabilize a bromine pool and make the bromine less and less effective. There is no method for measuring DMH levels like there is for CYA so you just have to be careful with using brominated spa tablets.

I would not count too much on the ozone system helping you out. The ozonators installed on hot tubs are often very cheaply made units that die very quickly (within a year) and there's no way to know if they are or are not producing ozone. Ozone, in theory, should also activate bromine but the units on hot tubs are so under-powered that you really can't tell if they are working or not.
When using household bleach to activate the bromine, what would you use to test the chem level and what number would you be looking for? I wish the pool math app had a caluculator that worked for this. If it does can you point me in that direction? Thank you!


TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
The standard DPD chlorine test is what is used. Technically speaking, the DPD indicator reacts with any halogen (chlorine, bromine or iodine) to form the pink color. All you do is change the multiplier used. 1ppm Cl2 is equivalent to 2.25ppm Br2. Since chlorine reacts instantly and completely to convert bromide to bromine, the assumption that there isn’t both chlorine and bromine present is good enough.

For a bromine hot tub, you typically want the sanitizer level to be somewhere between 4-8ppm Br. That’s typically sufficient to keep the water sanitary.

The PoolMath App has on its list of To Do’s to add in some simple bromine calculations. It’s just not a major priority because bromine isn’t really used in pools and a lot of hot tub owners here on TFP use chlorine in their tubs.