Dlleno's Bromine Plan

[dlleno]

Here is my "no puck no floater" bromine plan with ozone and borates for hot tubs. This plan is essentially the “dichlor then switch to bleach” method except that sodium bromide salts are in the water. Here is why I like it:

• my family likes Bromine better than Chlorine; we have no allergies or sensitivities.
• I have no interest in expensive alternative sanitizer methods. Bromine is cheap – especially if one uses bleach for the bromide conversion
• Ozone assists in contaminant oxidation and also in the bromine conversion itself, which means no floater is required even when leaving the spa unattended for long periods of time.
• pH control is a breeze

Optional prep work: use the pool calculator to determine the amounts needed:

1. Set aside the amount of dichlor that will produce ~35-40 ppm FC in the spa, i.e. about 1/2 cup for 500 gallons. This is my oxidizer until it is used up, at which time I have roughly 30-36ppm CYA, signaling it is time to switch to bleach. I note that with Sodium Bromide salts present in the water, I could skip the dichlor step and go straight to bleach, but this is extra insurance.
2. (Optional – if you are using borates to help buffer pH). Set aside the amount of Boric Acid that will produce approximately 50ppm (-0/+10) borates in the spa (for a 500 gallon spa, 3 cups of Boric Acid calculates to 58ppm borates). Yes, I'm a borates fan
3. Set aside the amount of sodium bromide that will produce 30ppm in the spa, i.e 2.5 ounces for 500 gallons

Initial fill:

1. I fill with straight tap water (with an outboard sediment filter attached to the garden hose), as my city water supply is very close to target balance numbers. Softened water or a combination of tap water and softened water can be used to achieve a lower CA level.

A note on heating: depending on the source water condition, the heater can be turned on as soon as the fill is complete enough, although I prefer to achieve water balance close to targets first.

2. Adjust CA level to target (120-150ppm) if needed. 130ppm is working well for me. If you must live with a significantly higher CA level, use the pool calculator to study the likelihood of a large positive CSI (in the event of pH swing), and consider using a scale control product regularly, per label directions. I like to use one for additional insurance.

3. Adjust TA to target, using Baking soda to raise TA (not likely you will need this) and the “acid+aeration” method to lower TA (run the jets to raise pH, then lower both pH and TA with dry acid). I target 50ppm TA with pH 7.6-7.8. Choose a target TA value that affords the best pH control over time, which you will learn from experimentation.

Water balance note: The method of controlling pH with a relatively low TA will require a higher CA to maintain a zero CSI. Nitro has reported good success with CA=200, TA=60, pH=7.8, which is dead on CSI=0 at 103 degrees (F) water temperature. Chem Geek tends to recommend a lower CA level, and reminds us that the CSI can be well below 0 for acrylic spas. My owner’s manual specifies a minimum of 50ppm Calcium to maintain warranty protection.

4. Add the Boric acid set aside earlier.

Note: Chem geek reminds us that Borates will soften the rate of an upward pH swing more so than a downward swing.

5. Turn on the heater if not done previously

6. Dose to ~10ppm FC (using dichlor).

Note on initial shock: This is a good opportunity to check FC decay rate (Note that sunlight, ozone, and agitation will cause FC to decay). YMMV, but I have learned that if I properly purge the OLD water first (dose with Ahh-Some and 10-20ppm FC before draining), and then immediately fill with my chlorinated tap water, that a high initial FC initial dose is unnecessary and I can start with a lower level, closer to 4ppm.

7. When the FC level drops to ~4ppm FC, I add 30-40 ppm Sodium Bromide from the quantity set aside earlier. This creates the bromide bank and converts the 4ppm FC to 9ppm Bromine. Dosing higher than 30-40 ppm sodium bromide is not necessary, but gives you insurance against bromide consumption or loss via splash-out. Dosing lower than 30ppm may result in a less than 100% bromine spa.

Note on adding Bromide salts: be sure to wait until FC has decayed to acceptable levels before adding sodium bromide, as your bromine decay rate (with ozone in use) will be even lower than with Chlorine. This is because, while ozone destroys free chlorine it actually helps convert bromide salts into bromine. With a clean spa and no sanitizer demand it can take days to drop the bromine level down to acceptable levels.

8. Enter the spa when temperature, water balance, and sanitizer targets are achieved.

Maintenance:

1. A strong, Corona Discharge Ozone generator should be able to maintain a non-zero Bromine level under ideal, no-load conditions in a 500 gallon spa. In my Hot Spring Grandee, I typically see levels ranging from “Just a hint of pink” in the FAS-DPD test, to 1.5 ppm.
2. I test regularly using the Taylor FAS DPD test for Bromine kit (2106).
3. I use MPS from time to time as my oxidizer, as its Bromine conversion rate is a little slower than Chlorine, and so it will behave as a native oxidizer for a bit longer.
4. Although this isn’t as important in a bromine spa, I start with dichlor as my oxidizer until achieving 40ppm CYA, and then I switch to bleach. Sometimes I switch to bleach early for the fun of it.
5. I purge with “Ahh-some” on every drain, and every time, the results confirm that it is beneficial to purge every time
6. I mix “Ahh-Some” in with a traditional filter degreaser to clean my filters.
7. To accommodate Bromide bank depletion I add an once or so of sodium bromide over life of the water just to be sure
   

[chem geek]

Sounds great and it works well because of the ozone that doubles as a bromide to bromine converter and an oxidizer of bather waste. Without the ozone, one would generally need to shock with chlorine on occasion.

Thanks for the excellent writeup!

[dlleno]

Glad to be of help. Just another point that was implied but not stated outright: MPS, dichlor, Bleach -- they all result in a bromine conversion with their own respective differences (however small they may be) which is why I change oxidizers from time to time.

really liking the above plan -- and the regular Ahh-Some purge at drain time is not nearly as painful as it might sound, and reaps great benefits! Its just part of my routine now. I wish folks could see what is lurking in their pipes even when things are maintained well. Especially revealing to me was the discovery that filters need the Ahh-Some as well.

[chem geek]

Not to put a damper on the approach, but I do want to make note of the fact that bromine produces more dangerous disinfection by-products than chlorine (see this post that shows the brominated DBPs being over 100 times more cytotoxic and over 10 times more genotoxic than their chlorinated DBP analogues). The absolute number is fairly low in both cases in a well-maintained residential pool or spa, but for those trying to minimize DBPs then chlorine is a better choice.

Chlorine and bromine smell differently so people have different preferences for them though they should be compared in a well-maintained spa since you don't want to be smelling chloramines (especially nitrogen trichloride) when using chlorine. Dosing after a soak avoids that for chlorine since you aren't in the tub while it is oxidizing most of the bather waste.

[dlleno]

Thats it -- I'm switching to iodine. hah hah hah!!

nice info. One downside of a bromine spa is that you can't use a "non bromine" shock, as the oxidizer will generate bromine from the reserve. Unlike a Cl spa, where you can shock with MPS - or shock with Cl but accelerate Decay with ozone.

As a practical matter, we haven't heard of any real danger posed by a bromine spa, but this info does give one pause. I'm just not able to translate this into, say, an equivalent drain interval (suppose you could drain the bromine spa more often and approach the equivent toxicity of Cl), because you would have to apply the factor of 100!.

So -- what happens to these DBPs over the live of the water -- do they simply accumulate?

[chem geek]

Potassium monopersulfate (MPS) non-chlorine shock oxidizes bromide to bromine slowly so if there are other chemicals to oxidize it will do so first. So MPS is still useful in a bromine spa for that purpose, though in practice most people find that shocking with chlorine helps clear the water better even though chlorine oxidizes bromide to bromine rather quickly.

As for the DBPs, the volatile ones outgas and accumulate under the cover so it's a good idea to air out the spa before you use it. The non-volatile ones build up in the water until you do a water change.