AN ACCURATE AND PRECISE METHOD FOR MEASURING IODINE

[Randy Holmes-Farley]

Some recent results show Iodine well above target levels in a couple of salt mixes (which is fine - it depletes)
I.O. and Reef Crystals checked in at 0.20ppm Iodine here.
https://www.reef2reef.com/threads/the-ultimate-salt-test.949805/post-10794608

(Also my I.O. made fresh is above 0.10 ppm Iodine too, so the results in the thread are consistent with what I've seen as well.)

Did you ever see a bump up just from a water change, and were there many water changes during this depletion curve?

What you feed (and, of course, what's in the tank, especially certain types of algae) may also make a big impact on the final steady state in the absence of dosing.

 

[Rick Mathew]

Some recent results show Iodine well above target levels in a couple of salt mixes (which is fine - it depletes)
I.O. and Reef Crystals checked in at 0.20ppm Iodine here.
https://www.reef2reef.com/threads/the-ultimate-salt-test.949805/post-10794608

(Also my I.O. made fresh is above 0.10 ppm Iodine too, so the results in the thread are consistent with what I've seen as well.)

Did you ever see a bump up just from a water change, and were there many water changes during this depletion curve?

So two things....I do a continuous water change...about 30%/Month ( 1.5gal/day) so I don't have occasion to see any big shifts due to water change. The water change amount was consistent over the testing period (30 days)...Second I use Red Sea Blue Bucket and for a while I tested every new bucket and found they were very consistent on their Iodine Level .....05 to .07 ppm....mostly at the upper end. So for sure the rate of depletion would be affected by the continuous water replacement.

 

[taricha]

And so now you get a good look at the depletion rate of the 0.06ppm Iodine in my tank.

One last demonstration of this method and Iodine trends in my tank. Here's showing the detected iodine input from water changes with a bag of Reef Crystals.
I did two 3 gallon changes in my 65 gallon system. So two x 4.5% water changes. The inputs are obvious and easily measured.

(this level of increase - 0.020 from 9% change implies Iodine of ~0.2ppm in the bag of reef crystals - which is in line with the collection of ICP results mentioned earlier.)

I.O. and Reef Crystals checked in at 0.20ppm Iodine here.
https://www.reef2reef.com/threads/the-ultimate-salt-test.949805/post-10794608

 

[Dennis Cartier]

Because the HI707 is not common in the reef stores, I started looking to see what else I have that uses a 525nm LED. I have a HI736 (ULR Phosphorous) and HI782 (Nitrate High Range). My question is does the compressed scale that other testers report in, compared to the HI707's 0-600 ppm, affect the resolution of the test substantially?

Update: It looks like I figured out the answer. The resolution of the HI782, 0 - 75.0, resolution of 0.1 ppm, accuracy +/- 2.0 ppm, +/- 5% of reading, compares well to the HI707, 0 - 600 ppb, resolution 1 ppb, accuracy +/- 20 ppb, +/- 5% of reading.

I just needed to shift the decimal place. :beaming-face-with-smiling-eyes:

 

[Dan_P]

Because the HI707 is not common in the reef stores, I started looking to see what else I have that uses a 525nm LED. I have a HI736 (ULR Phosphorous) and HI782 (Nitrate High Range). My question is does the compressed scale that other testers report in, compared to the HI707's 0-600 ppm, affect the resolution of the test substantially?

Update: It looks like I figured out the answer. The resolution of the HI782, 0 - 75.0, resolution of 0.1 ppm, accuracy +/- 2.0 ppm, +/- 5% of reading, compares well to the HI707, 0 - 600 ppb, resolution 1 ppm, accuracy +/- 20 ppb, +/- 5% of reading.

I just needed to shift the decimal place. :beaming-face-with-smiling-eyes:

I obtainec good results using the LR Phosphate Checker.

 

[Dennis Cartier]

A big thanks to @Rick Mathew , @taricha and @Dan_P for working this out. It is very helpful for monitoring iodine levels, especially when setting up daily dosing.

I found that iodine appears to accumulate and easily become elevated once I addressed the depressed level of iodine. Uptake of iodine appears to slow down dramatically once the historical deficit is addressed.

This test method has been invaluable for tweaking my daily iodine dosing.

 

[Rick Mathew]

A big thanks to @Rick Mathew , @taricha and @Dan_P for working this out. It is very helpful for monitoring iodine levels, especially when setting up daily dosing.

I found that iodine appears to accumulate and easily become elevated once I addressed the depressed level of iodine. Uptake of iodine appears to slow down dramatically once the historical deficit is addressed.

This test method has been invaluable for tweaking my daily iodine dosing.

You are most welcome...Really glad to see it is helpful to others in the community.

 

[taricha]

I found that iodine appears to accumulate and easily become elevated once I addressed the depressed level of iodine. Uptake of iodine appears to slow down dramatically once the historical deficit is addressed.

I can't say for sure if that's what's going on, but it does fit with observations. People who don't intentionally add iodine usually are depleted, and people who do add iodine according to a schedule without testing often find that their iodine is well higher than their intended target value.

 

[Rick Mathew]

I can't say for sure if that's what's going on, but it does fit with observations. People who don't intentionally add iodine usually are depleted, and people who do add iodine according to a schedule without testing often find that their iodine is well higher than their intended target value.

I agree that's been my experience...For me that was one of the motivators to have a more accurate test.

 

[Graham's Aquaculture]

I wanted to take a moment to give some recognition to Rick and all the hard work that went into developing this test procedure. I recently sent samples of my 3 systems and new salt batch off to the folks at Oceamo for ICP-MS testing. I also performed my usual home tests on the samples. I'm quite impressed to how closely the results matched:

Oceamo ICP-MS vs Ricks Method:
Instant Ocean Batch 23108: 115.2 vs 138 ppb
Reef System 1: 40.6 vs 42 ppb
Reef System 2: 34.4 vs 30 ppb
Reef System 3: 47.5 vs 45 ppb


It should be noted I am still using the 2021 method. But regardless, this method is a huge improvement considering some of the better test kits on the market basically have the resolution of looking at the color of a test result to determine if you're closer to 0, 30, or 60 ppb. Really great work here, Rick! Thanks so much.

 

[Graham's Aquaculture]

And thank you to @Dan_P and @taricha as well for their contributions to developing this method.

 

[Rick Mathew]

I wanted to take a moment to give some recognition to Rick and all the hard work that went into developing this test procedure. I recently sent samples of my 3 systems and new salt batch off to the folks at Oceamo for ICP-MS testing. I also performed my usual home tests on the samples. I'm quite impressed to how closely the results matched:

Oceamo ICP-MS vs Ricks Method:
Instant Ocean Batch 23108: 115.2 vs 138 ppb
Reef System 1: 40.6 vs 42 ppb
Reef System 2: 34.4 vs 30 ppb
Reef System 3: 47.5 vs 45 ppb


It should be noted I am still using the 2021 method. But regardless, this method is a huge improvement considering some of the better test kits on the market basically have the resolution of looking at the color of a test result to determine if you're closer to 0, 30, or 60 ppb. Really great work here, Rick! Thanks so much.

Thank you Sir very kind of you! as you have already noted @Dan_P and @taricha made significant contributions to the work. It is my (as well as others) belief that with proper care and good laboratory practices hobby grade test kits can yield equivariant if not better results than ICP testing...We are actually working on a project to make this comparison to see if our assumption is correct...we have already posted some early findings here (https://www.reef2reef.com/threads/how-do-you-ensure-accurate-wc-testing.990803/page-3#post-11481466) Thank you so much for the recognition and the confirming data!!

 

[SteveMM62Reef]

I always float both Vials with Water in them, so they will both be the exact same temperature.

 

[Rick Mathew]

I always float both Vials with Water in them, so they will both be the exact same temperature.

Not sure which vials you're talking about? Are you talking about for the Red Sea test?

 

[SteveMM62Reef]

Not sure which vials you're talking about? Are you talking about for the Red Sea test?

Yes, the Sample and Timing comparison.

 

[taricha]

I always float both Vials with Water in them, so they will both be the exact same temperature.

I do the same with the one sample I use. I hold the sample and reagents in a water bath to be certain the temp is what I think it is.
Wasted a lot of mine and Rick's time trying to figure out an error caused by cleaning my vial with a cooling solvent cleaner.

 

[Mickey]

I obtainec good results using the LR Phosphate Checker.

@Dan_P, @Rick Mathew, @taricha - do you think this test will work using the HI736 ULF Phosphorous, or the HI713 Phosphate testers? I happen to have those lying around.

 

[taricha]

@Dan_P, @Rick Mathew, @taricha - do you think this test will work using the HI736 ULF Phosphorous, or the HI713 Phosphate testers? I happen to have those lying around.

The hi736 won't work. The initial color is out-of-range-high, but the hi713 will work fine, the measurement will change a little bit, but not too much.
Rick has that checker and can probably comment on it more.

 

[Rick Mathew]

@Dan_P, @Rick Mathew, @taricha - do you think this test will work using the HI736 ULF Phosphorous, or the HI713 Phosphate testers? I happen to have those lying around.

As @taricha mentioned, the 713 should work fine. That being said I never ran a calibration curve for it. It is not likely that the regression that works for the HI-707 will work for the 713...you will most likely need to run a calibration set and generate a regression formula.

 

[Mickey]

Thanks for getting back to me. I may give it a try as I'm starting to dose Iodine in my 19 year old reef. Not sure I can handle Rick's suggestion for running a calibraton set and generating a regression formula. My chemistry class days are 50 years behind me but I'll review all the information in the article that initially went over my head and see if I can figure it out. Regardless, it sounds like using the HI713 will at least put me in the ballpark and prevent me from going much too high. Or, I can just pick up the 707 at Black Friday! what's one more tester? :beaming-face-with-smiling-eyes: