how to establish bromide bank with tablets.

FYI, you can order sodium bromide from online retailers. It's still legal and safe for use in spas, even in Canada, as long as it's not used with MPS, UV, or ozonation (and it needs to be labelled to that effect). It is hard to find in stores, but I've found some for sale from several online retailers.

I'm still interested in the answer to your question though, since it will take a few days for my sodium bromide to arrive and it would be nice to know how to establish a bromide bank in a pinch.

The two products I have are brominating concentrate and bromine tablets.

Brominating Concentrate:
- Sodium Dichloro-s-triazinetrione: 52.7%
- Sodium Bromide: 14.7%

Bromine Tablets:
- available bromine as 1-bromo-3-chloro-5,5-dimethylhydantoin and related hydantoins: 68.4%
- available chlorine as 1-bromo-3-chloro-5,5-dimethylhydantoin and related hydantoins: 28.2%

I found this comment on how much sodium bromide is needed (conveniently enough, for my spa volume of 420 US gallons):

JoyfulNoise said:

order to get 30ppm Br- bank in 420 gallons of water, you need about 61.3 grams or 2.2 ounces of sodium bromide. It's really not super necessary to be that accurate as the bromide bank is just there to act as a reserve of bromide ions so it could be 30, 40, 50ppm or whatever is easiest to add. 30ppm just ensures you have enough bromide in the water so that if you want to shock the tub, you can get up to the 20ppm bromine level easily. Bromide doesn't go away so you should only need to create the bromide bank once per fill and then it's good to go.

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Using brominating concentrate, I would need about 417 g of it to reach 61.3 g of sodium bromide. That's a lot of chemcial, especially since it contains ~200g of dichlor! That doesn't sound very convenient...

Using bromine tablets, there seems to be a much better ratio of available bromine to available chlorine, so that seems at a glance like the way to go. The only problem is, I'm not enough of a chemist to know what the ratio of bromine to bromide is... If it's 1:1, then adding 90g worth of crushed bromine tablets should result in a bromide bank of 30 ppm in my tub. Also, I'm not sure what 28.2% "available chlorine" would mean in terms of free chlorine levels, i.e. how much I can safely add in one batch.

Hopefully someone with a bit more chemical knowledge than me can confirm what that ratio is so we can do the math

Jonsstihl said:

I found some at canac but it is combined with another product. only 14% sodium bromide. so I'm wondering about the quantities to add. i don't want to send the CL over the top while waiting for the bromine to build up.

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You should be able to find 100% (or Darn near it) sodium bromide online. Again, that doesn't help us here and now, but it would be helpful to order some in advance for the next refill.

I did some digging and found this comment from chem geek:

chem geek said:

You are correct that if you created a 30 ppm bromide bank, then if you added chlorine or another oxidizer you could get up to a 30 ppm [EDIT] (actually, 60 ppm, if bromide is measured as Br- while bromine is measured as Br2) [END-EDIT] bromine level with any excess chlorine creating an additional chlorine level.

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So it seems that the ratio of bromine to bromide is 2:1, so I would need approx. 122 g of available bromine to become 61 g of sodium bromide, assuming all of the bromine is converted into sodium bromide. This works out to using 180 g of bromine tablets in my case, but I'm still not sure how many ppm of Cl that works out to.

However, a 2:1 ratio also means that in order to get a level of 20 ppm active bromine (shock level), only 10 ppm bromide should be necessary. I imagine that this process isn't perfectly efficient though, so it might be helpful to aim for 15 ppm initially. That brings me back down to 90 g of tablets, which is in line with the rule of thumb I've read elsewhere of "4-5 tablets" (20 g/tablet) for my size of tub. So that sounds sensible to start with.

Still, it would be helpful if someone with more knowledge could confirm my reasoning with more precision.

Here is the funny part.. We can get bromine easily here in the states and that is what I started out using.. I could never get it to work... I changed to dichlor to chlorine and loved it then went to SWG and LOVED it even more...

I like the idea of using a bromine floater to maintain my sanitizer levels while away for days at a time. SWG would be nice but then I'd have an electrode hanging from a cord all the time, and have to supply it with power, and that's not to mention the high up front cost, and the uncertainty of whether my heater is corrosion-resistant titanium. For now I'd like to give bromine a try.

Jonsstihl said:

finally got some sodium bromide and I think I want to try it. I am due for a drain and fill in about a month so if the bromine doesn't work out I can change fairly quickly.
I never did end up using the bromine 14.7% stuff I bought. So I have been running my spa on LC for more than a year but would like to at least try bromine once
is the 30 ppm by weight . I have 1 LB of sodium bromide but it is 99% so I am assuming I need very little. I will take a look at the bottle tonight.

I also have saltron mini that I plan to use but I don't have an outlet close to the spa to use yet (fall project) so I will start with bromine and LC then maybe switch to bromine and saltron and if the bromine doesn't work out I can alway switch to saltron and LC.

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I was wondering how this is working out for you? I had the same trouble of not being able to find Sodium Bromide locally.

I tried using both the tabs and granules. My thought was that it would basically be like using dichlor until the tabs built up enough of a bank. Unfortunately, that didn't work out for me as I end up dumping the water by the time enough tabs are finally dissolved.

So now I've found a source for Sodium Bromide online (which ironically is local, but no local pickups). I'm hoping it'll work better.

Although this tub I have is a constant problem. It is old (2003) and came with the house. I've tried everything under the sun (Ahh-some, trichlor, dichlor, liquid chlorine, SWG, new ozonator, new filters and now bromine), but around 2 weeks after a fresh fill and light usage we'll start coughing when the jets are open and it only gets worse from there.

I've been extremely diligent on maintaining proper levels, testing daily, no idea what I'm doing wrong. I am hoping bromine will help, or at least last a couple months between fills.