Which test to believe (FAS-DPD Bromine)?

[bacontrees]

Hi All,

Long time listener, first time caller.

I'm contemplating the switch from chlorine (SWG) to bromine, as I may have a chlorine sensitivity.

It's my understanding that I've created 30ppm bromine bank (3ppm FC, .2ppm CC per Taylor FAS-DPD, then added 69g NaBr to 430gal last night).

Since I've been running Cl for years, I already had plenty of DPD powder and R-0871 reagent on hand. I ordered and received some R-0872 for some convenience and also piece of mind as I try something new, but I understand I should be able to use either with the correct conversions.

I've seen a multiplier of 2.25 thrown out many places around here. I've read that if you use R-0871 you can use a multiplier of 2.25 to obtain bromine amount. reference

Results of this morning's FAS-DPD testing was as follows. All tests done at 25mL, so .5x R-0872, .2x2.25x R-0871:
4 drops R-0872, 3 drops R-0871 (2/1.35 by my math)
Add 1/3cup 6% bleach
7 R-0872, 7 R-0871 (3.5/3.15)
Add 1/3cup 6% bleach
7 R-0872, 7 R-0871 (3.5/3.15)
Add 1cup 6% bleach
17 R-0872, 15 R-0871 (8.5/6.75)
Waited an hour or two while starting this thread, eating lunch, etc
14 R-0872, 12 R-0871 (7/5.4)
The last test I did actually add the 5 R-0003 drops, and it did turn a touch pink. One drop R-0871 eliminated that. So perhaps some CC hanging around messing things up?

Any thoughts on why I consistently have this variance between the two tests? Is one of my reagents expired and less accurate perhaps? Is my NaCl content messing with anything? Am I just missing some maths?

I'll give full chem rundown in case at all relevant:

• 430gal, 101F
• ~40 TA (mine needs to be low, always has been, always has been stable at that)
• 7.8pH (my pH has always been high, hence 40 TA)
• ~150CH (naturally soft water, add CaCl upon fillup to achieve this)
• 1500ppm NaCl (coming from a SWCG)
• 15ppm CYA
• Borates -- can't remember if I ever added on this fill
• All measurements Taylor dropwise

It's probably time for a drain/fill, but honestly bather load has been next to nil since the last, my levels have been incredibly stable (thank you perfectly tuned TA and SWG ORP sensor), and I'd like to either confirm or deny my chlorine sensitivity before making the leap.

Thanks in advance for any guidance here!

@JoyfulNoise
@chem geek

 

[ajw22]

I don’t see a big variance in results. Pick one testing method and use it. As long as your results are within the broad ranges you should be good.

What model standalone spa is this?

Why do you mention “perfectly tuned TA and SWG ORP sensor” in a standalone spa?

 

[bacontrees]

I don’t see a big variance in results. Pick one testing method and use it. As long as your results are within the broad ranges you should be good.

It's not huge, but 10%-30% difference isn't nothing. I just want to know which one is the accurate test, as they should be the same. I was hoping someone could chime in on my conversion math to see if that's the issue. But I suppose I'll probably just order another bottle of reagent to solve this.

What model standalone spa is this?

Why would model matter, or just curious?

Why do you mention “perfectly tuned TA and SWG ORP sensor” in a standalone spa?

Why not mention details of my setup?

 

[ajw22]

I am trying to understand what your setup is and if we are discussing a standalone spa or a pool/spa combination. But I will go off to other things and see if others have answers for you.

We ask members to create their signature with details of their pool and equipment so we can see your setup at a glance while reviewing your messages...

Create Your Signature - Further Reading

www.troublefreepool.com

 

[bacontrees]

I am trying to understand what your setup is and if we are discussing a standalone spa or a pool/spa combination. But I will go off to other things and see if others have answers for you.

We ask members to create their signature with details of their pool and equipment so we can see your setup at a glance while reviewing your messages...

Create Your Signature - Further Reading

www.troublefreepool.com

Got it. Missed the nuance of the standalone vs pool/spa combo. Will create my signature now.