Bromine Start Question

[Jerry123]

In reading another thread, I suspect that I may be doing my chemistry incorrectly so I'd like to lay out what my scenario is and correct any mistakes. I'd like to get the Bromine scenario right before I explore alternatives.

OK, here we go

- have a 450g spa

- ozone generator

- floater (minimun setting)

with Brom-a-guard tablets (active ingredient: 1-bromo-3-chloro-5,5-dimethylhydantoin)

- Shock....I have been using Oxy-Spa which is 42.8% potassium peroxymonosulfate. It says on the container that this product is 100% Monopersulfate compound.

So, I read in a post that I am supposed to establish the spa with Sodium Bromide.

I don't remember this part last year when i first got the spa. Should I be adding sodium bromide at a water change? If so....what product and what quantity?

Thanks much

[chem geek]

waterbear (Evan) can probably answer this better than I can since I sometimes get this mixed up, but I believe the Brom-a-guard tablet you have is essentially a combined system that contains both the bromine and the chlorine in the same initial chemical. In other words, it is already equivalent to starting with sodium bromide and then adding chlorine or non-chlorine shock to activate it (and, I believe, having extra chlorine as well since I believe you will have both bromine and chlorine initially). The shock you are using is indeed the same as potassium monopersulfate (KMPS) as peroxymonosulfate is just a synonym for monopersulfate. The reason for the claim that it is 100% pure and yet only has 42.8% potassium preoxymonsulfate is that this compound is part of a larger compound that has potassium sulfate and potassium bisulfate in it (the compound is K2SO4•KHSO4•2KHSO5). The only truly "active" part of this compound is the extra oxygen found in that last part and is given up as SO5 converts to SO4 -- oxygen gets reduced (and takes away electrons from) other compounds that get oxidized. The rest of this compound mostly just adds potassium and sulfates to your water (and lowers the ph by adding hydrogen ions).

In your spa, the bromine will disinfect (kill bacteria and viruses) and prevent algae growth forming bromide while the chlorine will do the same and will reactivate the bromide to bromine and may also oxidize some compounds. When you add the shock, this will reactivate the bromide back to bromine. The shock will also oxidize organics. The Brom-a-Guard is acidic and the non-chlorine shock is very acidic so you will probably have to keep your TA up high enough to compensate (aeration from your spa jets will help make the pH rise to compensate the acidity of the products you add). If your pH still drops, then you'll need to add pH Up (sodium carbonate) to raise it.

So, bottom line, is that you already have what you need and do not need to get or add sodium bromide.

[Jerry123]

waterbear (Evan) can probably answer this better than I can since I sometimes get this mixed up, but I believe the Brom-a-guard tablet you have is essentially a combined system that contains both the bromine and the chlorine in the same initial chemical. In other words, it is already equivalent to starting with sodium bromide and then adding chlorine or non-chlorine shock to activate it (and, I believe, having extra chlorine as well since I believe you will have both bromine and chlorine initially). The shock you are using is indeed the same as potassium monopersulfate (KMPS) as peroxymonosulfate is just a synonym for monopersulfate. The reason for the claim that it is 100% pure and yet only has 42.8% potassium preoxymonsulfate is that this compound is part of a larger compound that has potassium sulfate and potassium bisulfate in it (the compound is K2SO4•KHSO4•2KHSO5). The only truly "active" part of this compound is the extra oxygen found in that last part and is given up as SO5 converts to SO4 -- oxygen gets reduced (and takes away electrons from) other compounds that get oxidized. The rest of this compound mostly just adds potassium and sulfates to your water (and lowers the ph by adding hydrogen ions).

In your spa, the bromine will disinfect (kill bacteria and viruses) and prevent algae growth forming bromide while the chlorine will do the same and will reactivate the bromide to bromine and may also oxidize some compounds. When you add the shock, this will reactivate the bromide back to bromine. The shock will also oxidize organics. The Brom-a-Guard is acidic and the non-chlorine shock is very acidic so you will probably have to keep your TA up high enough to compensate (aeration from your spa jets will help make the pH rise to compensate the acidity of the products you add). If your pH still drops, then you'll need to add pH Up (sodium carbonate) to raise it.

So, bottom line, is that you already have what you need and do not need to get or add sodium bromide.

Thank you for you're input.

Does this mean that if I put sodium bromide in the spa I can get rid of the bromine tab floater?

[chem geek]

Yes, if you add bromine to your pool by adding sodium bromide and then adding either chlorine or non-chlorine shock (KMPS) to activate it (i.e. to convert the bromide to bromine), then you can replace your floater. However, you will need to stay on top of your bromine level and keep it at 10 ppm (you should have a bromine test kit). You will need to regularly (probably daily or every other day) add chlorine and/or shock to reactivate the bromide back to bromine and occassionally you may need to add more sodium bromide (but probably not very often as bromide/bromine tends to stay in the spa rather well -- unlike chlorine that tends to leave quickly). The floater is more convenient as it continually introduces more "already activated" bromine into your spa, but it's really up to you as to which method you prefer.

Another sanitation option is to just use chlorine alone. This would make sense if you had any irritation or sensitivity to bromine (some people do). To use chlorine alone, you would start (after a fresh drain and refill of the spa) by using Dichlor about 3-4 times (assuming each addition was equivalent to 4 ppm of chlorine) and then you would switch to using unscented bleach thereafter (until the next drain and refill in a few months).

You've got alternatives -- the choice is up to you.

[waterbear]

Here are some quick answers to your questions. 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 dissolve. Some people crush about 6 of them up and put them in the water on each water change to achieve this but it really is easier and cheaper to add a packet or two of sodium bromide! It is available from such compaines as HTH, Leisure Time, Robarb (Rendezvous), and others. Chem geek is right in that the bromine tablets contain both bromine and chlorine to oxidize the bromine into active sanitizer.

There are basically 2 ways to do a bromine system--2 step and 3 step. In the 2 step system you add the sodium bromide to the water to the proper concentration, then add oxizider on a regular basis (usually, chlorine, MPS, or ozone, or a combination of them) to oxidize the bromide ions into hypobromous acid, your active sanitizer. It's pretty easy but does require a bit of attention daily to maintain the bromine levels in the water.

A 3 step system is identical with the addition of bromine tabs in a floater. This will help maintain a more constant bromine level in the water with less maintenance but otherwise there is no difference. The three step system costs more since the bromine tablets are the most expensive part of this equation. The dimethylhydantoin in the tablets seems to have a similar (but not identical) function in a bromine system as CYA does in a chlorine system. It tends to stablilize it but, like CYA, too much is not good. Not that much info is readily available on the effects of dimethylhydantion other than that it makes the bromine more difficult to destroy, a consideration if you ever want to switch over to a chlorine system.

If you add sodium bromide to your water and have an ozonator you might be able to achieve the constant bromine level without the floater since the ozone is constantly oxidizing the bromide while it is on. However, you might deplete the bromide reserve quickly this way, leading to a shorter time between drain and refills. You still need to superoxize (shock), usually about once a week to destroy organics in the water. I prefer plain, unscented laundry bleach for shocking a bromine spa. 1 cup per 250-300 gallons is about right.