Hanna Phosphate Checker HI713

[IURobert]

Hi all!

I have this Hanna Checker HI713 for Phosphate, the low range one. My issue here is that when i test, at the first reading after timer ends i have one reading, let’s say 0.26 ppm and as i always check twice, at the second reading i have always half or less from first reading. I perform the second reading without the timer. Is there something i do wrong or can be the checker or something else?
Thank you!

 

[KStatefan]

Why are you not using the timer for the second test?

 

[IURobert]

Why are you not using the timer for the second test?

Because i think that timer is just for the solution to take effect and the color to settle witch was already done at the first reading.

 

[Garf]

I perform the second reading without the timer

You are waiting 3 minutes though? No?

 

[IURobert]

You are waiting 3 minutes though? No?

Yes, I use the checker timer for the frist reading. You have to long press the button at C2 step to start the timer. For the second check i don’t use the timer as those 3 minutes have already passed once.

 

[Garf]

Yes, I use the checker timer for the frist reading. You have to long press the button at C2 step to start the timer. For the second check i don’t use the timer as those 3 minutes have already passed once.

So you’re not doing the whole test again on a different water sample? You appear to be pressing the button randomly until you get another reading. The calibration step C1 for example, how are you doing that? A fresh sample, or just skipping over it with the previously tested sample?

 

[IURobert]

So you’re not doing the whole test again on a different water sample? You appear to be pressing the button randomly until you get another reading. The calibration step C1 for example, how are you doing that? A fresh sample, or just skipping over it with the previously tested sample?

No, i am doing it as is reauested. Step C1 with a non reacted sample from aquarium and the C2 with reacted solution. I have made a lot of test with different Hanna checkers for different parameters. The only thing i don’t do at the second reading is to start the timer. First reading to me means that i complete a Phosphate check with C1 and C2 step as instructions request to and the second read is when i repeat those steps to see if i get the same reading with the same reacted solution, without throwing the jars content. Hope i’m clear now.

 

[FishTruck]

It is normal that if you throw off the timing by testing with two different controls... and reading the same reacted solution twice, you will get different results. I always use the three minute final timer too.

 

[Randy Holmes-Farley Verified Community Expert]

I'm a bit confused about what you are doing, but the colored phosphate solution is not stable and is not expected to keep reading correctly as more and more time passes.

 

[Dburr1014]

OP is doing the test as normal the 1st time.

2nd time he is using a cuvette filled with aquarium water to calibrate then re-using the sample from the 1st test.

Correct OP?

Randy is correct, the sample is no longer stable after... 6 minutes(maybe longer) when your 2nd test is finally completed.

 

[taricha]

(short answer: I think OP is switching the C1 "blank" cuvette, and thus getting a different reading on the reacted sample.)

Longer: If you used the same cuvette as the C1 blank for the timed test and the immediate re-test, then the results would be very much the same.
But if you use a cuvette as C1 blank, then react it, measure the reacted sample (correct). and then to "re-check" use a different cuvette as C1 blank and remeasure the reacted cuvette, then you will get a different result due to slight variations in how the two cuvettes behave.

 

[Eagle_Steve]

(short answer: I think OP is switching the C1 "blank" cuvette, and thus getting a different reading on the reacted sample.)

Longer: If you used the same cuvette as the C1 blank for the timed test and the immediate re-test, then the results would be very much the same.
But if you use a cuvette as C1 blank, then react it, measure the reacted sample (correct). and then to "re-check" use a different cuvette as C1 blank and remeasure the reacted cuvette, then you will get a different result due to slight variations in how the two cuvettes behave.

This right here.

The purpose of doing an unreacted test with the cuvette is to account for any deviations in that cuvette. Using cuvette 1 to assume cuvette 2's deviations is no good.

It is also good to orientate the cuvettes in the same way as when test 1 (unreacted) is completed. I do this via making sure the letters on the cuvette always face forward (at the display)