Testing bromine levels in hot tub. How long to wait?

[RobbW]

I have a Marquis e750 hot tub. I use a Lamotte ColorQ test kit to test my water chemistry. When I test for the bromine level, I add the 5 drops to sample and invert the tube several times before inserting into the ColorQ reader. My bromine levels always test really low; usually less than 1ppm. However, if I let the test tube sit there for anywhere from 1-5 minutes before testing again, the bromine level always ends up testing even higher; anywhere from 2ppm-9ppm depending on how long it sits.

How long should I wait to test the bromine level after adding the reagent? Should the accurate test results be the one I get immediately after adding the reagent and giving it a good shake? Should I use the results I get after letting the test tube sit for 1 minute, 2 minutes, 5 minutes, etc.? All the other tests don't appear to increase or change much after letting the tubes sit for several minutes (e.g. pH, Alkalinity, Carbonate Hardness).

I use a bromine sanitizing system and my spa has an ozone system, if any of that matters to my question.

Thanks,
Robb

 

[JamesW]

For bromine, most kits say that you only test total bromine vs free and combined as you do with chlorine.

Theoretically, combined bromine should show up in the first part of the test and you should not get a result in a combined test.

This is due to the formation of the monobromammonium ion (NH₃Br⁺), which disassociates into ammonia and bromine (NH₃ + Br⁺).

However, it has been my observation that there is almost always a reaction in a combined test in a bromine test.

I don't know what is reacting, maybe bromamines, mps, ozone, bromate, bromoform, bromodichloromethane, dibromochloromethane etc.

When using bromine, a variety of brominated disinfection byproducts can be formed. Monobromamine should react right away, but many of the other compounds might not react as easily. Others might need iodide (R-0003) to be added to get a reaction.

I would use fas-dpd to do a free and combined test to determine the total oxidizer in the water.

Also, try to minimize the use of bromine tabs to reduce the buildup of dmh (the carrier compound for bromine, which is analogous to CYA in a chlorine tub).