Bromine Chemistry Question

[eGGnog]

Hey all. So I am getting my above-ground spa in order using the bromine system and I am a little concerned about a few things. So far, I have emptied, cleaned and refilled tub. I balanced the spa. pH 7.4, TA 40, CH 100. I then threw in a packet of sodium bromide and just over 1/2 cup of 8.75% concentrated bleach. I tested with the FAS-DPD test a few hours after adding bleach and 24 hours later and it came out to FC 11 both times. Assuming we multiply that by 2.25 that means I am at 24.75 for bromine? According to the bromine sticky, I shouldn't enter the spa until that number gets below 10. Based on what I have seen so far that seems like it wont be for some time. Is that normal? Also, when I do the FAS-DPD test, when the water goes from pink to clear it has a bit of a yellowish haze. That seemed a bit odd to me as well. Any thoughts? Thanks.

 

[chem geek]

What size is your spa? Also, wasn't the bleach 8.25% in concentration, no 8.75%? 1/2 cup of 8.25% bleach would raise the FC to 11 ppm in around 250 gallons.

Does your spa have an ozonator? If so, then ozone will make more bromine from the bromide bank so you won't find the bromine level dropping and could even find it increasing depending on the amount of ozone and the size of the bromide bank.

If you need to lower the chlorine/bromine level, you can add 3% hydrogen peroxide in the same volume as 6% bleach for the FC amount you want to drop. [EDIT] This only works for chlorine. This will probably not work for bromine because hydrogen peroxide also oxidizes bromide to bromine. It is unclear what the equilibrium amount of bromine will be as a result. [END-EDIT]

 

[eGGnog]

Oops, you were right. 8.25% is correct. Not 100% sure on the spa size but I guesstimated 350 gallons. I am guessing I overestimated it's size based on the chemistry math. I do not think the spa has an ozonator. Thanks for the hydrogen peroxide tip.