Hanna Phosphate Help

[CheifReeferNB]

I have recently battled inconsistent phosphate readings which were inexplicably fluctuating throughout the day. I suspected it may be my methods.

When I use a vial of tank water as the blank and follow the test procedure as normal. I get a reading of 0.16- 0.19ppm.

When I use the “blank” cuvette that comes with the phosphate standard kit as the C1 baseline and use a separate vial for the reaction with tank water, I get a phosphate reading of 0.09. It is very consistently 0.09 as well.

I would figure the latter reading should be higher since the blank has no cloudiness to set a baseline for light passing through.

Could my sample cuvette be damaged or stained causing the inconsistency and elevated readings? Let me know what you guys think and if you have any experience with this.

 

[Bucrob]

I have recently battled inconsistent phosphate readings which were inexplicably fluctuating throughout the day. I suspected it may be my methods.

When I use a vial of tank water as the blank and follow the test procedure as normal. I get a reading of 0.16- 0.19ppm.

When I use the “blank” cuvette that comes with the phosphate standard kit as the C1 baseline and use a separate vial for the reaction with tank water, I get a phosphate reading of 0.09. It is very consistently 0.09 as well.

I would figure the latter reading should be higher since the blank has no cloudiness to set a baseline for light passing through.

Could my sample cuvette be damaged or stained causing the inconsistency and elevated readings? Let me know what you guys think and if you have any experience with this.

Any fingerprints or markings on the glass of the cuvette?

 

[CheifReeferNB]

I have recently battled inconsistent phosphate readings which were inexplicably fluctuating throughout the day. I suspected it may be my methods.

When I use a vial of tank water as the blank and follow the test procedure as normal. I get a reading of 0.16- 0.19ppm.

When I use the “blank” cuvette that comes with the phosphate standard kit as the C1 baseline and use a separate vial for the reaction with tank water, I get a phosphate reading of 0.09. It is very consistently 0.09 as well.

I would figure the latter reading should be higher since the blank has no cloudiness to set a baseline for light passing through.

Could my sample cuvette be damaged or stained causing the inconsistency and elevated readings? Let me know what you guys think and if you have any experience with this.

There’s scratches for sure. Could be the source of the problem. No fingerprints. Still a little confused why the blank sample would induce a lower reading. I would figure the light diffraction from scratches would be normalized with using the same cuvette (to a certain extent).

 

[KrisReef]

Test should follow

Fill cuvette with tank water to be tested.

Zero the meter with that water, remove, add reagent, shake for 2 full minutes, replace in meter and start the three minute timer. The meter will read and report results after 5 minutes.

The vial needs to be aligned in the meter in the same location as the zero'ing was done to get best results.

 

[EnterName]

Have you tried using RO/DI instead of an empty vial for C.1? I wouldn't rely on the results but it would be an interesting test to see if the meter is broken.

Even though the photometer just measures light intensity, I could imagine the refractive index difference when using air vs. water in the vial can mess with the amount of light getting into the sensor.

 

[CheifReeferNB]

Have you tried using RO/DI instead of an empty vial for C.1? I would rely on the results but it would be an interesting test to see if the meter is broken.

Even though the photometer just measures light intensity, I could imagine the refractive index difference when using air vs. water in the vial can mess with the amount of light getting into the sensor.

I don’t use air. I use an unreacted sample of tank water. Using rodi water is essentially what I’m doing when I use the standards sample as that is a solution Hanna certified as a “zero”.

 

[Randy Holmes-Farley Verified Community Expert]

I would use the real vial test as directed, oriented the same way every time, not anything else. Switching vials may lead to oddities due, as you suspect, to differences in the vial itself or the contents. Even glass thickness differences might change the nature of light passing through a curved vial.

Real spectrometer’s nearly always use square cuvettes and would not have the odd scattering effects of a curved surface in the light path.

 

[Dan_P]

I have recently battled inconsistent phosphate readings which were inexplicably fluctuating throughout the day. I suspected it may be my methods.

When I use a vial of tank water as the blank and follow the test procedure as normal. I get a reading of 0.16- 0.19ppm.

When I use the “blank” cuvette that comes with the phosphate standard kit as the C1 baseline and use a separate vial for the reaction with tank water, I get a phosphate reading of 0.09. It is very consistently 0.09 as well.

I would figure the latter reading should be higher since the blank has no cloudiness to set a baseline for light passing through.

Could my sample cuvette be damaged or stained causing the inconsistency and elevated readings? Let me know what you guys think and if you have any experience with this.

If you are curious about how the reference standards vary, in separate experiments use each in C1 and the other during C2. You will get a reading if the reference standard in C1 is more transparent than the reference standard in C2 , and an error message when it is higher. Repeat each comparison 3 times to check for variability. In a separate experiment, deliberately change the orientation of the C1 reference standard vial keeping the C2 vial exactly the same to see if the vial is affecting the results. There are more ways to explore this test.

 

[CheifReeferNB]

I would use the real vial test as directed, oriented the same way every time, not anything else. Switching vials may lead to oddities due, as you suspect, to differences in the vial itself or the contents. Even glass thickness differences might change the nature of light passing through a curved vial.

Real spectrometer’s nearly always use square cuvettes and would not have the odd scattering effects of a curved surface in the light path.

Wouldn’t it be reasonable to expect a higher reading using the standard blank as the C1 baseline. That’s the part confusing me.

 

[Randy Holmes-Farley Verified Community Expert]

Wouldn’t it be reasonable to expect a higher reading using the standard blank as the C1 baseline. That’s the part confusing me.

You assume the difference is absorbance from the tank water compared to the blank. I do not know if there is much absorbance at the wavelength used, but if the issue is different scattering from the curved surface, or scratches, or something like that, then it could go either way.

In any case, doing something that is not in the directions that gives a different value may be a fruitless thing to pursue.

 

[CheifReeferNB]

Wouldn’t it be reasonable to expect a higher reading using the standard blank as the C1 baseline. That’s the part confusing me.

You assume the difference is absorbance from the tank water compared to the blank. I do not know if there is much absorbance at the wavelength used, but if the issue is different scattering from the curved surface, or scratches, or something like that, then it could go either way.

In any case, doing something that is not in the directions that gives a different value may be a fruitless thing to pursue.

I have new curettes coming in to eliminate potential wear as an issue. Ultimately I fear the problem is Hanna is trying to achieve lab grade results with toy grade hardware. The variability in these tests upon the mildest change makes them almost useless in my opinion.

 

[Randy Holmes-Farley Verified Community Expert]

I’ve not personally noticed much variability in the Hanna phosphate test I use.

 

[winxp_man]

Test should follow

Fill cuvette with tank water to be tested.

Zero the meter with that water, remove, add reagent, shake for 2 full minutes, replace in meter and start the three minute timer. The meter will read and report results after 5 minutes.

The vial needs to be aligned in the meter in the same location as the zero'ing was done to get best results.

This right here. I set my index to the cuvette as follows. Align the 10ml writing with the right side tongue device. Which there is also a slight visible seam line being it’s where the two half’s of the reader meet.

 

[BryanM]

I do the test as described above.

When wiping down the cuvette, after I hold it up to the light to make sure it is dry before zeroing or testing.

I always rinse with RODI, and when done testing I always fill with RODI for storage.

 

[Natman2]

Hanna is a ball park test kit just like all the others and keep in mind a three foot bunt and a 350 fly out to center field are both in "in the ball park". Your best test kit is your eye balls/daily observation of your tank for and hour or so every day. That's why my small tank is next my bed and I can lay down and watch it for and hour or so before I go to sleep. Then again you can't impress the neighbors with a tank like that.

 

[Randy Holmes-Farley Verified Community Expert]

Your best test kit is your eye balls/daily observation of your tank for and hour or so every day.

I’m not sure I agree with that. Tank observation is all fine, but when things are not looking ideal, how would you know what the issue might be?

FWIW, I use a diy alk test that is quite accurate, at least for reefing purposes.

 

[CheifReeferNB]

Just as an update, it seems my LFS has sold me batches of reagent which should have been recalled. Both boxes are Lot 1250 and Lot 1352, I noticed today when I opened a new packet and the powder was purple.

Unfortunately just another reason to shop online nowadays…