Help with hanna phosphate checker

[Optionman]

I meant; to the person who started to thread.................

Ooops. Sorry


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[pisanoal]

Another good reason to use two cuvettes. Ive done it too, but I tested my cuvettes and refraction difference is minimal. So if you forget, you can re-zero and immediately test the reacted sample.

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[pisanoal]

Post error...

 

[pisanoal]

As stated above, that is not the optimal procedure and the differences in the two vials will effect the test results.

I stated this earlier too, but you can check your cuvettes before writing this option off. Fill both with the same water, zero 1, read 2. Then zero 2, read 1. If both read 0.00 ppm, difference will not cause noticeable error.

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[Tripod1404]

I stated this earlier too, but you can check your cuvettes before writing this option off. Fill both with the same water, zero 1, read 2. Then zero 2, read 1. If both read 0.00 ppm, difference will not cause noticeable error.

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That is no way of doing it. You assumes error you get at zero is linearly proportional to the error you get at the measurement. Which is absolutely not, it is exponentiation. Beer–Lambert law used to make these measurements is A= b*L*c, where A is absorbance, b is the molar extinction coefficient of the solute, L is path length and c is concentration. And A is actually the log10 (or power of ten) difference of absorbance of blank and sample. Non of these calculations are made as additions, they are all multiplications.

Device basically measures the absorbance (A) and since L and b are constants, it calculates the concentration (c) and rounds it to the nearest integer. Since the device doesn't give you the absorbance but the calculated concentration, you cannot now if two vials both give the equal absorbance. And it is impossible for two vial to give equal absorbance, even quartz vial that are far more uniform than regular glass vials wont give equal absorbance.

As a result of these, even if the measured absorbance values are different, if the calculated values are close enough, they can be rounded to one and other. For example if the calculated concentration is 0.4 ppb, the device will round that to 0 and give you the fake impression that both vials read the same. It is the reason why the device only gives full integers, it never outputs 0.6 ppb or 2.7 ppb, it rounds those numbers to the nearest integer. But this would only happen at low values. A negligible difference of 0.4 ppb at low absorbance values can turn into 5-10 ppb at higher absorbance values. So a 0ppb vs. 0.4ppb at blanking can become 25 vs. 32 at measurements, that is a 30% error.

The only way of using two vials interchangeability is to get matched pair vials, which are produced as one big vial and than divided into two, and these are not made from glass but made from quartz. That is the closes you can get to identical vials.

 

[pisanoal]

That is no way of doing it. You assumes error you get at zero is linearly proportional to the error you get at the measurement. Which is absolutely not, it is exponentiation. Beer"“Lambert law used to make these measurements is A= b*L*c, where A is absorbance, b is the molar extinction coefficient of the solute, L is path length and c is concentration. And A is actually the log10 (or power of ten) difference of absorbance of blank and sample. Non of these calculations are made as additions, they are all multiplications.

Device basically measures the absorbance (A) and since L and b are constants, it calculates the concentration (c) and rounds it to the nearest integer. Since the device doesn't give you the absorbance but the calculated concentration, you cannot now if two vials both give the equal absorbance. And it is impossible for two vial to give equal absorbance, even quartz vial that are far more uniform than regular glass vials wont give equal absorbance.

As a result of these, even if the measured absorbance values are different, if the calculated values are close enough, they can be rounded to one and other. For example if the calculated concentration is 0.4 ppb, the device will round that to 0 and give you the fake impression that both vials read the same. It is the reason why the device only gives full integers, it never outputs 0.6 ppb or 2.7 ppb, it rounds those numbers to the nearest integer. But this would only happen at low values. A negligible difference of 0.4 ppb at low absorbance values can turn into 5-10 ppb at higher absorbance values. So a 0ppb vs. 0.4ppb at blanking can become 25 vs. 32 at measurements, that is a 30% error.

The only way of using two vials interchangeability is to get matched pair vials, which are produced as one big vial and than divided into two, and these are not made from glass but made from quartz. That is the closes you can get to identical vials.

I am quite aware of all of that actually. We are not attempting an analytical method. I don't really care if my reef is 25 vs 32 ppb of phosphate. The differences at the range of values we care to measure would either be quite small or not significant if the meter did output a rounded down value of zero. Most of the time, especially with phosphate, we are more interested in comparative values and trends then hard numbers anyways. If you always use vial 1 for blank and vial 2 for reacted sample the error will be the same. For the error you gave, that equates to 0.1 (0.098) vs 0.08 (0.078) ppm. I highly doubt you are going to see much of a difference in your reef there. Most people recommend a ppm target of somewhere around 0.03 ppm phosphate (10 ppb) where your percent error is going much lower.

If you are really that concerned about the relatively minor error then run an actual test on water you like your reef in using the vials in both orientations and find out how different the values are. I've done this several times with no appreciable difference in measurement.

Please note, I'm not saying you are wrong, your explanation is accurate. I'm well aware of the principles involved and referenced the fact that matched pairs are available a for lab spectrophotometers and better when swapping between two vials. I just don't believe the minor error that can be induced from doing this is worth worrying about for this particular application (phosphate in a reef tank).

 

[Tripod1404]

I am quite aware of all of that actually. We are not attempting an analytical method. I don't really care if my reef is 25 vs 32 ppb of phosphate. The differences at the range of values we care to measure would either be quite small or not significant if the meter did output a rounded down value of zero. Most of the time, especially with phosphate, we are more interested in comparative values and trends then hard numbers anyways. If you always use vial 1 for blank and vial 2 for reacted sample the error will be the same. For the error you gave, that equates to 0.1 (0.098) vs 0.08 (0.078) ppm. I highly doubt you are going to see much of a difference in your reef there. Most people recommend a ppm target of somewhere around 0.03 ppm phosphate (10 ppb) where your percent error is going much lower.

If you are really that concerned about the relatively minor error then run an actual test on water you like your reef in using the vials in both orientations and find out how different the values are. I've done this several times with no appreciable difference in measurement.

Please note, I'm not saying you are wrong, your explanation is accurate. I'm well aware of the principles involved and referenced the fact that matched pairs are available a for lab spectrophotometers and better when swapping between two vials. I just don't believe the minor error that can be induced from doing this is worth worrying about for this particular application (phosphate in a reef tank).

Yeah it ultimately comes down to how precise you want the results to be. Like you said, if it is just for an overall measurement, it can be fine. But in my case, I was as interested in the change with respect to the previous measurement, as the value itself.

I basically recorded the all the data and make trend analysis on it. Like the consumption/generation rates. At one point i was even recording the grams and type of food I added each day. I was able to correlate those to changes in nitrate and phosphate. So I would only make phosphate and nitrate measurements once a week to "correct" the deviation of the model. Ultimately it gave me a good idea about how much NO3 and PO4 was present within the system at any given point. Like if I fed a lot of frozen food one day, I know how much less pellet food I needed to feed the next day and etc. I no longer to this since my N and P levels has been consistently very low (below 1 ppm NO3 and 0.01 ppm PO4) for a very long time and dont seem to change much.

So for me the measurements needed to be as identical to each other as possible. Call me paranoid but I even marked my vials so the go into the reader in exactly the same orientation, because I dont think a glass vial can be homogeneous across all its surface.

 

[pisanoal]

Yeah it ultimately comes down to how precise you want the results to be. Like you said, if it is just for an overall measurement, it can be fine. But in my case, I was as interested in the change with respect to the previous measurement, as the value itself.

I basically recorded the all the data and make trend analysis on it. Like the consumption/generation rates. At one point i was even recording the grams and type of food I added each day. I was able to correlate those to changes in nitrate and phosphate. So I would only make phosphate and nitrate measurements once a week to "correct" the deviation of the model. Ultimately it gave me a good idea about how much NO3 and PO4 was present within the system at any given point. Like if I fed a lot of frozen food one day, I know how much less pellet food I needed to feed the next day and etc. I no longer to this since my N and P levels has been consistently very low (below 1 ppm NO3 and 0.01 ppm PO4) for a very long time and dont seem to change much.

So for me the measurements needed to be as identical to each other as possible. Call me paranoid but I even marked my vials so the go into the reader in exactly the same orientation, because I dont think a glass vial can be homogeneous across all its surface.

Yeah... That is definitely a much more advanced application than most, and I can definitely see where absolute accuracy is more important for a project like that. Really cool idea.

I didn't mark my vials, but I face the 10mL mark straight out every time. Not perfectly the same, but close enough.

 

[LeJeune981]

I've been experimenting differant things since I started the post.. using all of the suggestions as well... I think I've got it down pact now. I think lol

I have noticed... it says add 10 ml of water to the tube .. and that should fill it to the level of the marked line of 10 ml

But.. when I use the 5ml syringe from my sailfert Phos test kit.... the water level is always above the marked line by about 1/16th of an inch..

Is that normal or should I only be filling to the line they provide... and it's very possible I am using the syringe wrong... I've never used a syringe before this hobby..

I suck the water in... put it upside down and tap put bubbles.. then while upside-down I push water out until I hit the 5 ml line..

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[Optionman]

I would draw fluid into the syringe until the bottom of the stopper is at the line. The liquid will not always draw all the way up to the line as the air in the syringe compensates for the fluid in the tip of the syringe. I think your way leads to more fluid and thus the 1/16 excess.

Hope this helps, not sure my explanation is the best.


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[LeJeune981]

I would draw fluid into the syringe until the bottom of the stopper is at the line. The liquid will not always draw all the way up to the line as the air in the syringe compensates for the fluid in the tip of the syringe. I think your way leads to more fluid and thus the 1/16 excess.

Hope this helps, not sure my explanation is the best.


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I understand what you mean.. in the sailfert mag test kit.. it has you suck the reagent into the syringe the same way..and says the air inside is already compensated for

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[pisanoal]

I understand what you mean.. in the sailfert mag test kit.. it has you suck the reagent into the syringe the same way..and says the air inside is already compensated for

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Not sure if you know this already or not, but you read the bottom most curve of the water. It should be right in the center where one if the gaps in the line is. I would go by the vial's mark.

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[swiftvision]

Mine gave me false readings since new. Almost ruined my tank.

I think they are garbage IMHO.

 

[Tripod1404]

Mine gave me false readings since new. Almost ruined my tank.

I think they are garbage IMHO.

I dont think so, I got very reproducible results with Hanna Phosphate checker and I was able to verify the results with other methods (like ICP/triton).

IMO Hanna phosphate checkers are the single most accurate device on market for phosphate. And the level of accuracy of any test kit is orders of magnitude lower.

If you got false results you either had a defective device (or us, bad reagents or you made an error.

 

[pisanoal]

I dont think so, I got very reproducible results with Hanna Phosphate checker and I was able to verify the results with other methods (like ICP/triton).

IMO Hanna phosphate checkers are the single most accurate device on market for phosphate. And the level of accuracy of any test kit is orders of magnitude lower.

If you got false results you either had a defective device (or us, bad reagents or you made an error.

I agree 100%. The only times I've found my checker to be inaccurate are when my lamp started failing (which it gave me warnings), user error, and I've noticed as the alk reagent gets down towards the bottom, it shows falsely high (only a few tenths and I'm not sure if it has something to do with opening the bottle up repeatedly or what but ive noticed it over the past 3 or so reagent changes).

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[LeJeune981]

Agreed.. I've double checked with my sailfert kit.. and always get a similar reading..
I am thinking of getting a couple different hanna checkers

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