Testing with same hanna reagent?

[KochergenJ]

Might be a stupid question about hanna checkers, but here it goes.

Was running a test on the nitrate hr checker and got a result of 46 ppm. Seeing as this test was a few hours after a roughly 20% water change, I assumed it was a bad test. Pulled the vile and noticed small bubbles throughout, figured it caused a bad result.

Got a clean vile, zeroed the test again, retested the same original sample, new result was 22.8 ppm. Performed the same procedure and got 23.0 ppm.

Can you use the same reagent multiple times as I did above and get accurate results?

 

[KrisReef]

I have found that my Checkers will give repeatable results when I am careful to use proper technique each time.
When I get weird results I retest to see if it was me or the tank that is off.

 

[KrisReef]

The exception to this may be dKH if the reagent is getting old. It is known to fade after being opened and used for a long period. I open a new reagent to see what is up if the bottle is older and the results are unexpected.

Stability is expected so deviation requires validation.

 

[Randy Holmes-Farley]

Can you use the same reagent multiple times as I did above and get accurate results?

What do you mean by the same reagent?

 

[KochergenJ]

What do you mean by the same reagent?

Opening up 1 packet of reagent, placing that into the sample container, and running multiple tests on that sample, say 3 times to get an average .

 

[Randy Holmes-Farley]

Opening up 1 packet of reagent, placing that into the sample container, and running multiple tests on that sample, say 3 times to get an average .

I am confused. I've never used this kit, but if we are talking about the HI 781, in looking at the directions, I do not see a step where there is "left over" reagent from one test that you might be using for a second test later.

https://www.hannainst.com/hubfs/product-manuals/IST781_09_20.pdf?hsLang=en#:~:text=Remove%20the%20cuvette%2C%20unscrew%20the,shake%20vigorously%20for%202%20minutes.&text=Insert%20the%20cuvette%20into%20the%20checker%20and%20close%20the%20cap.&text=Press%20and%20hold%20the%20ON%2FOFF%20button.

 

[KochergenJ]

I am confused. I've never used this kit, but if we are talking about the HI 781, in looking at the directions, I do not see a step where there is "left over" reagent from one test that you might be using for a second test later.

https://www.hannainst.com/hubfs/product-manuals/IST781_09_20.pdf?hsLang=en#:~:text=Remove%20the%20cuvette%2C%20unscrew%20the,shake%20vigorously%20for%202%20minutes.&text=Insert%20the%20cuvette%20into%20the%20checker%20and%20close%20the%20cap.&text=Press%20and%20hold%20the%20ON%2FOFF%20button.

Sorry, my bad on the explanation.

So I put 10 ml into a vile. Place the entire packet of reagent into the vile. Shake for 2 minutes, I know have my test sample.

With a second vile, I go pull 10 ml of tank water, no reagent in this vile, this is now my "zeroing" solution for the test.

Can you run the test sample multiple times or do you need to empty it out after each test and open a new packet of reagent?

 

[Reef Wizard]

I am confused. I've never used this kit, but if we are talking about the HI 781, in looking at the directions, I do not see a step where there is "left over" reagent from one test that you might be using for a second test later.

https://www.hannainst.com/hubfs/product-manuals/IST781_09_20.pdf?hsLang=en#:~:text=Remove%20the%20cuvette%2C%20unscrew%20the,shake%20vigorously%20for%202%20minutes.&text=Insert%20the%20cuvette%20into%20the%20checker%20and%20close%20the%20cap.&text=Press%20and%20hold%20the%20ON%2FOFF%20button.

I think he maybe is referring to using the same cuvette and reacted sample again after testing it once. Instead of using another unreacted sample and new reagent. pardon my chemistry french lol not sure of all the terms but I try

 

[Uncle99]

Opening up 1 packet of reagent, placing that into the sample container, and running multiple tests on that sample, say 3 times to get an average .

You can do that but nitrate will darken over minutes which may lead to incorrect assumptions.

At 2 minutes, the shake time, it will have coloured up, in the next 7 minutes, the wait time, the colour will intensify, so if you retest at say 10 mins, the result may be higher. There would be a point where the colour has fully developed.

If a test comes back largely outside your “expected” result, just rerun the full test again.

There are many ways tests come out incorrect.

 

[KochergenJ]

I think he maybe is referring to using the same cuvette and reacted sample again after testing it once. Instead of using another unreacted sample and new reagent. pardon my chemistry french lol not sure of all the terms but I try

Bingo!

 

[Reef Wizard]

Bingo!

I have done this a couple times before for my own testing purposes but its always been close but if its way different id just rerun a new unreacted sample and reagent

 

[KochergenJ]

You can do that but nitrate will darken over minutes which may lead to incorrect assumptions.

If a test comes back largely outside your “expected” result, just rerun the the test.

You can do that but nitrate will darken over minutes which may lead to incorrect assumptions.

If a test comes back largely outside your “expected” result, just rerun the the test.

That is what I was unsure of. If the sample continues to darken over time or not. To run 3 tests would be roughly 21 minutes as the tester takes 7 minutes to perform. Wasn't sure how the "sample" would react over that duration.

 

[Uncle99]

That is what I was unsure of. If the sample continues to darken over time or not. To run 3 tests would be roughly 21 minutes as the tester takes 7 minutes to perform. Wasn't sure how the "sample" would react over that duration.

After 7 minutes we would expect colour to be mostly developed, so if retested at 14 minutes, the results should be close.

All your really doing is asking the Hanna to recheck the colour.

The colour will only darken so far regardless of time, so if I did a second check, I’d do it as close to the 7 minutes as possible.

 

[DanyL]

I do this from time to time with the Phosphate ULR test.

However, instead of “press and hold” to start the timer, I do a regular press which samples immediately, and it needs to be done rather quickly.

This only applicable when there was a problem with the vial itself, like a missed air bubble or an accidental smudge you’ve only noticed after the fact and caused the result to be invalid.

 

[Randy Holmes-Farley]

I'd be wary of repeating the absorbance measurement at longer and longer times to try to get a better reading as many of the tests we use are not stable. Some companies explicitly say what window of time is acceptable and what is not.

The Hach nitrate kit says, for example:

"Allow at least 10 minutes, but not more than 20 minutes, before..."

 

[KochergenJ]

I do this from time to time with the Phosphate ULR test.

However, instead of “press and hold” to start the timer, I do a regular press which samples immediately, and it needs to be done rather quickly.

This only applicable when there was a problem with the vial itself, like a missed air bubble or an accidental smudge you’ve only noticed after the fact and caused the result to be invalid.

I had missed a lot of air bubbles and realized after the test results. Got rid of those bubbles, ran it twice after and results were within .02 ppm.

 

[DanyL]

I had missed a lot of air bubbles and realized after the test results. Got rid of those bubbles, ran it twice after and results were within .02 ppm.

If the vials were shaken between the tests it’ll likely affect the results as well, wether it being the reaction itself or by indissolved powder floating around inside the sample.

For air bubbles, when I miss them it’s usually just one or two, and slightly rotating the vial in a way that the sensor won’t be abstracted by it is enough.

For smudges I do the same when possible, otherwise I carfully clean it without disturbing the sample in the process.

I’ve done this quite a few times, and when done correctly it aligns perfectly with my trends.

 

[Reefer Matt]

Yes you can do that so long as it is not hours in between tests, as the results may not be accurate. In fact, if you miss the countdown and the checker turns off, you usually don’t need to retest with new reagent. Just fill another cuvette with tank water, zero it out (C1), then put the original colored sample in for C2. Press the button instead of holding to get an immediate result.

The length of time the reagent can sit in the cuvette is debatable (I will ask Hanna), but if you just missed the timer by a few minutes or so, this will save you some reagent. You can also retest with the same filled cuvettes to get an average, but the results should be very close.

Here’s a video so you don’t have to take my word for it, but I have also tested this myself.