Bromine / Liquid chlorine shock, testing for water safety

[MaxAcceleration]

I'm new to using Bromine for my hot tub and have a few questions:

I filled my 130 gallon hot tub and built up a proper 3-5ppm bromine level. Then I added CYA to 40ppm to buffer the bromine, incorrectly assuming bromine needed CYA protection - I now know differently, but just letting you know the CYA is in there.

Weekly I use liquid chlorine to bring to shock level to 15ppm based on my CYA.

Questions:
1.) After I shock with liquid chlorine how do I know what is reading on the test as free chlorine (left over from the shock) -vs- the actual bromine amount (free chlorine * 2.25)? For instance If I shocked in the morning bringing the water to 15ppm. I tested it at later in the day and get a 10ppm result. So should I take that as a 10ppm free chlorine level (which would be safe) or 10ppm * 2.25 = 22.5ppm bromine level (which would be unsafe), or some combination of the two?

2.) Once I have a established a 3-5ppm and shock weekly to return the bromide to bromine, is it true I don't need to add any further bromine (outside of splash out or evaporation) since it refreshes? ie... no needs for bromine tabs/floater?

3.) Related to question 1, how long before I can safely assume the test results are bromine and not chlorine - so I know whether I need to do the 2.25 math?

I use the Taylor K-2006C for testing as noted in my signature.

Thanks in advance,
Jamie

 

[ajw22]

Have you read…

How do I use Bromine in my Spa or Hot Tub?

Originally Posted by waterbear There is a lot of misinformation on the proper way to use Bromine so I hope this primer is helpful. First, you need to establish a bromide reserve in the water. Bromine tablets can do it by themselves but it can take literally weeks until enough dissolves. Some...

www.troublefreepool.com

You always have to multiply your FC by 2.25 to determine your bromine level.

 

[MaxAcceleration]

You always have to multiply your FC by 2.25 to determine your bromine level.

I did read the sticky post on Bromine. However, if I only add 1 tiny grain of bromine (as an extreme example) and enough chlorine to bring me to 10ppm then the bromine level certainly isn't 10 * 2.25 = 22.5ppm with only 1 grain of Bromine added. This test isn't specifically for Bromine and that's what's confusing when using bromine to sanitize and chlorine to shock. Which is why I asked the question.

 

[ajw22]

You are asking about an edge case. Put enough bromide into the spa and then chlorine activates the bromine.

 

[MaxAcceleration]

You are asking about an edge case. Put enough bromide into the spa and then chlorine activates the bromine.

I used an edge case to show the example that you can't just multiple FC * 2.25 to get a bromine level as you claimed. Since Chlorine/Bromine have different PPM of safe levels, it's important to be able to differentiate between chlorine and bromine when testing to determine of it's safe to enter the water. Something this method doesn't appear to be capable of doing, which is why I asked my questions. In addition to water safety, I also have a question (#2) about the reactivation and whether a continuous supply of Bromine needs to be added, or if it just reactivates after a chlorine shock treatment.

 

[ajw22]

If you are worried then you should stick to a chlorine spa.

There is no test for bromine only that can differentiate from chlorine.

 

[ajw22]

In addition to water safety, I also have a question (#2) about the reactivation and whether a continuous supply of Bromine needs to be added, or if it just reactivates after a chlorine shock treatment.

No. You do not need to continuously add bromine once you build the bromide bank in the water.

Bromine changes back to bromide when it does sanitation.

Then adding chlorine changes the bromide back to bromine to activate it again.

 

[Mdragger88]

Weekly I use liquid chlorine to bring to shock level to 15ppm based on my CYA.

The cya doesn’t matter if you have added any appreciable amount of bromide - your shock level is 10ppm Total Br

Questions:
1.) After I shock with liquid chlorine how do I know what is reading on the test as free chlorine (left over from the shock) -vs- the actual bromine amount (free chlorine * 2.25)? For instance If I shocked in the morning bringing the water to 15ppm. I tested it at later in the day and get a 10ppm result. So should I take that as a 10ppm free chlorine level (which would be safe) or 10ppm * 2.25 = 22.5ppm bromine level (which would be unsafe), or some combination of the two?

You can’t- there’s no way to differentiate between br & fc

Once bromide is in the water any chlorine you add becomes bromine.

2.) Once I have a established a 3-5ppm and shock weekly to return the bromide to bromine, is it true I don't need to add any further bromine (outside of splash out or evaporation) since it refreshes? ie... no needs for bromine tabs/floater?

I’m assuming you meant adding more sodium bromide-
Once your bromide bank is built up you are done adding it aside from splashout replacement.

3.) Related to question 1, how long before I can safely assume the test results are bromine and not chlorine - so I know whether I need to do the 2.25 math?

If you mean while you’re building up the bank with tabs - you need to know how much bromide is in the tabs so you can calculate how many it will take to build the bank. It usually takes a couple weeks depending upon how quickly they dissolve.
You can post the ingredients list here & we can help you calculate how much you have already added.