Question about a bromide bank

[Sjde]

What would happen if there was no bromide bank- if bromide wasn’t put in on a fill? Would you not be able to shock it to an adequate level?

 

[JoyfulNoise]

Are you using bromine tablets?

Basically, without bromide, you’d just have whatever oxidizers you put in the water. So if it’s bleach, you’d have chlorine in the water when you “shock” the tub. If you use non-chlorine shock, then you’d have monopersulfate in the water. If you use ozone to regenerate the bromine then you would have a minuscule amount of ozone in the water (it has very low solubility).

The “bromide bank” provides the bromide ion (Br-) needed for an oxidizers to convert bromide to sanitizing bromine. Too little bromide and you just get a mix of oxidizers in the water, some of which are not capable of adequately protecting against disease transmission (ie, persulfate and ozone).

 

[Sjde]

We are using MPS and bromine tabs.

 

[JoyfulNoise]

What’s the main ingredient of the bromine tablets.

 

[Sjde]

I'll have to check but I think most are Bromochloro-5, 5-dimethylhydantoin . And I guess they all have a little chlorine in them.

 

[JoyfulNoise]

I'll have to check but I think most are Bromochloro-5, 5-dimethylhydantoin . And I guess they all have a little chlorine in them.

BCDMH contains both chlorine and bromine. Both are released into the water where the chlorine oxidizes any excess bromide into bromine. Tablets will build up bromide levels very slowly. If you are using MPS to oxidize the excess bromide into bromine for shocking and there isn’t enough bromide around, you’ll get a mixture of bromine and persulfate in the water. Establishing the bromide bank up front just ensures that your water always has enough bromide in it so that shocking with an oxidizers will create the needed bromine levels.

Tablets are not a good way to establish the bromide bank. Better to just use granular sodium bromide for that purpose.

 

[Sjde]

Yes, I realize all this and our standard procedure is to build a bromide bank. The reason i asked the question is because this last time I suspected the service person had inadvertantly left it out (maybe had a new helper with them?), because I think there should have been no packets left and there was one left. So I wondered if there was some way to tell ( other than just asking them), by how the spa was reacting. I am there every 2-3 weeks and I check it . I wondered if I was in doubt, could I just add a packet, or can it be overdone?

 

[JoyfulNoise]

You can add as much sodium bromide as you like, it’s inert until an oxidizer converts it to bromine. So even if you have 100ppm sodium bromide in the water, if you only add enough bleach or MPS to generate 4-6ppm bromine, then that’s all that it will create. The oxidation/reduction reaction of chlorine and bromine happens quickly and completely - 1 mol of chlorine oxidizes 1 mol of bromide into bromine. The chlorine gets reduced from chlorine to chloride. Chloride is inert and no longer reacts with anything.

 

[Sjde]

The Maxibrom slow dissolving bromine tablets say they have 67% available bromine and 25% available chlorine .

Leisure Time (doesn’t say slow- dissolving so it’s regular or fast dissolving ) says it has 141% available bromine & 63% available Chlorine.

Caribbean Spa slow dissolving bromine tabs say 65% available bromine and 29% available chlorine.

Not sure what the implications are for all of that. Can anyone enlighten me as to what differences I can expect to see in my spa using one or the other?

 

[Sjde]

You can add as much sodium bromide as you like, it’s inert until an oxidizer converts it to bromine. So even if you have 100ppm sodium bromide in the water, if you only add enough bleach or MPS to generate 4-6ppm bromine, then that’s all that it will create. The oxidation/reduction reaction of chlorine and bromine happens quickly and completely - 1 mol of chlorine oxidizes 1 mol of bromide into bromine. The chlorine gets reduced from chlorine to chloride. Chloride is inert and no longer reacts with anything.

Thank you!