API PO4 Test With Hanna Checker & iPad Colorimeter

[Dan_P]

A common complaint about colorimetric tests is matching test color to the one on the chart. API's phosphate test is a challenge for me so I used two methods, the Hanna Checker (ULR) and an iPad/iPhone colorimeter app, to "read" the color of test solutions for a series of PO4 standards. The results are displayed in the photographs.

The take away message is that the PO4 API test is fairly sensitive and the Checker seems to provide less noisy data, though to be a fair comparison, I will need to perform replicates.

Hanna Reading

Colorimeter Reading

 

[GMay]

That is fairly nice. The only problem is that for most systems you want to operate at very low range < 0.1 ppm where there is not very good linearity. What app did you use for this? Can you test it in the 0 to 0.1 ppm range? That is more useful.

 

[Dan_P]

That is fairly nice. The only problem is that for most systems you want to operate at very low range < 0.1 ppm where there is not very good linearity. What app did you use for this? Can you test it in the 0 to 0.1 ppm range? That is more useful.

Agree with all your points. I am thinking about establishing the lowest detection limit. With the Hanna checker, it might be close to the Hanna limits but probably not with the colorimeter app.

Here's a picture of the app

 

[acesq]

I'm confused by the Hanna chart. Did you test known samples with the Hanna Phosphorous ULR checker HI736 and report them on the x axis? The reason I ask is it does not appear that the the Hanna ppb readings correspond to the y axis ppm. Isn't the conversion from ppb to ppm x3.066/1000? I must be missing something here.

 

[Dan_P]

I'm confused by the Hanna chart. Did you test known samples with the Hanna Phosphorous ULR checker HI736 and report them on the x axis? The reason I ask is it does not appear that the the Hanna ppb readings correspond to the y axis ppm. Isn't the conversion from ppb to ppm x3.066/1000? I must be missing something here.

Yes, a bit confusing. I used PO4 standards and the API test kit, with some modifications. I used the Hanna Checker to provide a number for each test solution. The plot I provided is calibrstion curve which connects the Hanna number to the API test color intensity. When I use the API test kit, the Hanna reading is meaningless without the calibration curve.

 

[acesq]

How did the Hanna perform relative to the standards?

 

[Dan_P]

How did the Hanna perform relative to the standards?

I looked into that here

http://www.reefcentral.com/forums/showthread.php?t=2474804

 

[acesq]

I looked into that here

http://www.reefcentral.com/forums/showthread.php?t=2474804

How did you calculate the Hanna ULR "ppb P" numbers in your chart? The checkers (at least mine) only read in whole numbers.

Also, you used spiked tank water for the standards in your January tests? Was that seasoned as opposed to freshly mixed? Is that the same way you prepared the standards for this test?

 

[Dan_P]

How did you calculate the Hanna ULR "ppb P" numbers in your chart? The checkers (at least mine) only read in whole numbers.

Also, you used spiked tank water for the standards in your January tests? Was that seasoned as opposed to freshly mixed? Is that the same way you prepared the standards for this test?

While the Checker reads in whole numbers, I typically take three readings and average them. The Checker reading can bounce around a little. I got into the habit of taking three readings. A good calibration curve will have triplicate tests for each standard. The one I post was only a demo, consisting of only one test result at each concentration.

I now use new salt water that can be one to several days old to make standards.