Shelf Life Of Sodium Bromide?

[njmurvin]

I recently drained and decontaminited my 350 gal Marquis spa (because of little white flakes floating after running jets on high). After the refill, I added a 2 oz packet of sodium bromide that I bought about 1 1/2 years ago. It was packaged in a metallic-like wrapper and sealed. I use a bromine floater and it's set to a level that has worked with this spa for a couple of years. For some reason, the bromine is only holding for a couple of days - as if the floater is not working. The spa has only been used once since the refill and I shocked it right after (7oz 6% bleach). I do have a ozonator but it only runs about 4 hours/day during filtration.

Is it possible that the sodium bromide I put in went bad on the shelf? Would it hurt to purchase another package and add it?

If my ozonator quit, is this what I would see? I considered the ozonator next to worthless on my spa because it runs so infrequently.

My pH seems to be running a little high as well (7.8 - 8.0). Can that have an effect on the bromine levels? Last I checked the TA was around 50.

[chem geek]

2 ounces of sodium bromide in 350 gallons would be (1000 mg/g) * (56.7 grams ) * (79.904 g/mole Br) / (102.894 g/mole NaBr) / (1325 liters) = 33 ppm bromide. The normal dosing is 1/2 ounce per 100 gallons so your 2 ounces should have been OK.

I would have thought that the shelf life of sodium bromide was similar to that of sodium chloride table salt so indefinite, but several sources give shelf lives of 1-2 years and some say that it does not have a very good shelf life. I suspect this may vary depending on the purity of the product and whether the packaging remains air-tight.

Anyway, it sounds like it didn't work well so just add some fresh sodium bromide and see what happens.

The pH shouldn't be a factor. And yes, if the ozonator quit, then you'd find that you are producing less bromine. If a fresh addition of sodium bromide doesn't work, then it's more likely that your ozonator stopped working.

[njmurvin]

Thanks. I'll pick up a new packet and give it a shot. If that doesn't fix it, I'm not sure I want to fix/replace the ozonator. Instead I'll probably just experiment with opening the floater up more. It's barely cracked open (maybe 3/4 inch) but that's all it has needed in the past to keep up (with a presumably working ozonator).

[arches2]

It could also be that your decontamination was only partly successful and you've freed up some extra sanitizer demand that needs to be killed off. Not saying it's likely but just wanted to throw that out there.

[njmurvin]

I considered that. Do you think the decon could have released more bad stuff into the water than was there before? I ask because the floater/bromide had no trouble keeping up before the decon when I would have expected the worst condition of the water.

[njmurvin]

As a followup ... I purchased and added another 2oz of Sodium Bromide and shocked with MPS. Bromine went up to 10. I also opened my floater to about 1 1/2 inches and the bromine levels seem to be holding (around 7 on Saturday). I closed the floater a bit. Even my pH came down (presumably the acidic effect of opening the floater and exposing more water to the tablets).

While I'm here, what is the shelf life of bleach? I have a bottle that I use exclusively for the spa and it's at least a year old (stored indoors in a cabinet in my laundry room). Is that too long?

[chem geek]

For bleach and chlorinating liquid, see the table at the bottom of this link. Now that's for high quality product with minimal metals to degrade the product, but you can see that the shelf life varies roughly with the square of the concentration so bleach will last longer than higher concentration chlorinating liquid. You can also see that keeping the product cooler has it last longer. A year is still quite a long time, however. You can always test it with a known amount to see if it's still good.