How To Do The Taylor Bromine Test And Interpret An Odd Result

[Jankjo]

I have two related questions about the Taylor Bromine test.

Question 1

The instructions say to add two scoops of the powder.

If Bromine is present the solution turns pink.

then add the other chemical drop wise until the solution turns clear.

I also read here that if the water turns pink after one scoop, I don't need to add another

AND

The instructions also say that if the water doesn't turn pink to add more powder

So does the amount of powder just not matter as long as the water turns pink? Or am I confused about the directions.

Question 2

I am currently switching from a bromine tub to an N2 tub in a quest to get rid of a rash I get on my arms every time I use the tub.

On Saturday I drained and refilled the tub.

I balanced the water

CH 160

TA 100

pH 7.6

after it heated all the way up, I added the N2 Cartridge and 1Tbs and 1 tsp of Dichlor (175 gallon tub)

On Sunday the FC was still high. (I am reading this on a test strip because my Taylor test kit for Chlorine has not arrived yet)

On Monday the FC was normal.

I added a scant Tbs of MPS so I could use the tub. The Mps level went too high (again read on a test strip). I was impatient to use the tub, and I read that I could use some chlorine neutralizer, so I added some hydrogen peroxide in the hopes that the MPS level would come down.

It did, and I used the tub.

After using the tub I added 1.5 tsp of MPS and the MPS level was good to high, but the chlorine was gone (probably from the hydrogen peroxide). So I added another Tbs of Dichlor and the FC level went back up.

But I noticed on my test strip that I had a 4ppm of Bromine. How on earth. I had just drained and refilled the tub? How on earth could I have bromine?

So I used the Taylor test kit. I added 4 scoops of the powder, and I measured a bromine level of 7?

I figure that either I am doing something wrong with the bromine test OR that some other chemical is causing a false reading.

Any help figuring this out would be very much appreciated.

[waterbear]

To answer your first question...No, you are not confused about the directions. The amount of DPD powder is not critical as long as you have a stable pink color. You need enough DPD powder to react witht the halogen (bromine or chlorine) present to form the Wurster dye (the pink color you see). This is your 'indicator'. The titrant (that you add drop by drop) is a reducing agent (halogen "neutralizer') and when it reacts with all the available halogen the Wurster dye disappears (since there is no halogen left).Excess DPD powder has no effect on the results and if you have added enough to form a stable pink color you have enough. If you don't add enough (so there is excess halogen in relation to the amount of DPD powder) the the Wurster dye gets 'bleached out to a colorless imine. Adding more DPD powder shifts this chemical reaction back so the Wurster dye forms and you are able to do the titration.

To answer your second question...The same tests are used for both free chlorine and bromine but use different scales. If you tested 4 ppm bromine then you had about 2 ppm chlorine mps. MPS tests as total chloirne, btw. Also, with the N2 system your santizer is MPS and silver, not chlorine, so you will not have any chlorine reading at all unless you have just shocked the tub. (but remember that MPS tests as CC!) .FWIW, you could use your Taylor FAS-DPD bromine test and divine the results by 2.25 to get your FC reading (or just by 2 for a ballpark figure that should be more than close enough!). In other words, if you test with the bromine test and get 8 ppm bromine with a 10 ml sample (recommended) then you have about 4 ppm FC (3.5 ppm in reality but since the accuracy of the test is 1 drop then 4 ppm is certainly within spec, since 1 drop equals about .5 ppm FC !)