Testing a bromine pool after a chlorine shock

What is floc, clarifier, stabilizer, cyanuric acid,
algaecide, brightener, dichlor, sodium hypo,
sodium bisulfate, ....??
SgtBilko
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Testing a bromine pool after a chlorine shock

Postby SgtBilko » Fri 28 Dec, 2012 05:01

Merry Christmas everyone !!! I hope someone is around this morning (UK time !) to help.

I have an indoor 67500 litre pool and use Bromine (via a brominator) as a sanitizer. After a lot of use over Christmas I shocked it yesterday with Chlorine shock. For once I did not read my log (I keep details of all past treatments) and put 1Kg of shock in (I usually use 1/2 Kg).

I turned off the Brominator last night and 18 hours later my photometer (Exact micro 10) produced a reading of 7.0.

But here is my problem .... the instructions say "Bromine result is the sum reaction of Bromine and Bromamine. Because the Bromine is measured in the CL3 MENU (DPD-1 test) you must multiply the Chlorine result, on the display by 2.6."........So I have a reading of 7.0 x 2.6 = 18.............. unsafe ?

Before I shocked I had a reading of .99 x 2.6 = 2.5

I have visitors today and want to use the pool. I was just about to dump and replace a whole load of water when I paused for thought.

Given the Bromine reading before the shock was 2.5, the reading of "18" must be down to Chlorine shock. So isn't the right reading (with no 2.6 multiplier) 7.0 ? i.e. within the 15 safety margin ?

So no need to drain and refill water ?

Your help would be appreciated.
Thank you


chem geek
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Testing a bromine pool after a chlorine shock

Postby chem geek » Sat 29 Dec, 2012 16:20

First of all, the multiplier to use to convert from chlorine units to bromine units is 2.25, not 2.6. When you add chlorine to a bromine pool or spa, you still end up with bromine and not chlorine because there is likely spent bromine (i.e. bromide ions) in the pool that will get oxidized by chlorine to make bromine. That is, the chlorine gets used up converting bromide to bromine.

Your 7.0 ppm chlorine reading is therefore equivalent to 7*2.25 = 15.8 ppm bromine, but these are both high levels (well, the chlorine reading wouldn't necessarily be high if there were Cyanuric Acid in the water).

Instead of draining/refilling with water, I would just directly lower the bromine level by adding a chlorine/bromine neutralizer. You can buy some at your pool store (usually it's sodium thiosulfate or similar reducing agent). If you had a chlorine pool then you could use hydrogen peroxide to reduce the chlorine level, but I don't think that will work for a bromine pool.
SgtBilko
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Testing a bromine pool after a chlorine shock

Postby SgtBilko » Sun 30 Dec, 2012 04:09

Thank you for your reply.

It is coming down of its own accord, 4.8 this morning. In any event there are no pool shops local and open this weekend, so I can't get hold of any neutralizer.

Where did you get the 2.25 figure from ? The instructions with the Exact say 2.6. I am not arguing with you (I don't know enough !!), but it would be good to know your source before I take your advice.

Thank you once again, much appreciated
chem geek
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Testing a bromine pool after a chlorine shock

Postby chem geek » Sun 30 Dec, 2012 04:28

Maybe your particular test kit has some differential measurement between chlorine and bromine, but standard DPD and FAS-DPD test kits can't tell the difference. So there is only a unit of measurement difference that is based on the molecular weight difference between chlorine (Cl2) at 70.906 g/mole vs. bromine (Br2) at 159.808 g/mole. 159.808/70.906 = 2.2538 so roughly 2.25. The simple DPD test kits just show two scales with one having values 2.5 times the other for simplicity so 2 ppm chlorine shows as 5 ppm bromine, but technically 2 ppm chlorine is 4.5 ppm bromine.
SgtBilko
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Posts: 6
Joined: Fri 28 Dec, 2012 04:19
My Pool: 67500 litres
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Testing a bromine pool after a chlorine shock

Postby SgtBilko » Sun 30 Dec, 2012 05:17

Thank you, that's interesting.

I have emailed manufactures (Sensafe - Industrial Test Systems Inc) for an explanation. I will, out of interest, post it when I have it.

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