SWG and bromine

[Tom RI]

I bought a house this past winter and it has an in-ground pool. The former owners used bromine. I have been using chlorine, as guided by the advice on these forums. And the pool water looks and tests fine. Because we are away from the house for 5 days every week, I have had some challenges trying to keep chlorine levels stable during those absences. A couple people on these forums have suggested a salt water generator. As I look into it, some SWG suppliers say you should not use their SWG until bromine levels are very low. I don't want to get a SWG and then screw it up because there's Br in the water.

So my question is how do I know if the Br level is very low? For example, there have been times when my FC level (using the TFT-100's OTO and FAS/DPD reagents) has been undetectable. Am I right that those tests measures both Cl and Br? And if the level was undetectable, does that mean there's no Br in the pool?

Thanks for your help.

 

[JasonLion]

It isn't easy to measure the bromide level, which is what matters here. You can get an approximate result by letting the FC/Br level fall to zero and then adding MPS. MPS will convert bromide to bromine, but not show up in the test it's self, and you can then test the bromine level. That approach has some pitfalls, but still works as a fairly good is there bromide or not check.

 

[Tom RI]

What is MPS? Is it a reagent that's in my TFT-100 kit?

Then after adding MPS, how do you measure bromine? With the standard OTO or FAS/DPD.
Thanks your help.

 

[JasonLion]

MPS is the most common kind of non-chlorine shock, technically potassium monopersulfate.

You can measure bromine with the FC portion of the FAS-DPD test.

 

[Tom RI]

I don't have any MPS. But I guess I could run the test you propose using hydrogen peroxide as the oxidizing agent, right?
I'll try this out the next time I find the chlorine level undetectable. I'll report the results here.

Thanks again Jason.