Neptune Aquatics

inconsistent results from Hanna 774 phosphate tester.

Joseph Lee

Joseph Lee

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I recently watched a youtube video talking about the Hanna 774 tester's inconsistency where he does at least 4-6 tests.
I tried the same and also got similar results. Are there also any other instances of this?
I am thinking about switching to the Phosphorus PPB version.

Pls see the results highlighted in red, I prepared two cuvettes, one with tank water and the other with mixed.
1st test: 3min
2nd test: single press (no waiting)
3rd test: single press ( no waiting)
4th test: 3min
1664161625323.png
 
Joseph Lee said:
I recently watched a youtube video talking about the Hanna 774 tester's inconsistency where he does at least 4-6 tests.
I tried the same and also got similar results. Are there also any other instances of this?
I am thinking about switching to the Phosphorus PPB version.

Pls see the results highlighted in red, I prepared two cuvettes, one with tank water and the other with mixed.
1st test: 3min
2nd test: single press (no waiting)
3rd test: single press ( no waiting)
4th test: 3min
View attachment 42235
Click to expand...

I’m not saying this is the problem, but you should try testing again using the same cuvette and be sure insert the cuvette in the same position every time. The length of the optical path will differ in two different cuvettes and can vary even in the same cuvette if not place in the same way.

Also, what’s the purpose of trying to do the test without holding down the button and waiting three minutes? The reagent needs time to react.
 
RandyC said:
Also, what’s the purpose of trying to do the test without holding down the button and waiting three minutes? The reagent needs time to react.
Click to expand...
I used the same cuvette only for the first test (in the same position), and for the 2nd, 3rd, and 4th tests, I prepared a new cuvette with tank water to set C1, and after that, the old cuvette (mixed with regent already) was reused for the result.
Next time, I will test 3-4 times only using the same cuvette (in the same position), with new regents. They will all be 3min tests.
 
Joseph Lee said:
I used the same cuvette only for the first test (in the same position), and for the 2nd, 3rd, and 4th tests, I prepared a new cuvette with tank water to set C1, and after that, the old cuvette (mixed with regent already) was reused for the result.
Next time, I will test 3-4 times only using the same cuvette (in the same position), with new regents. They will all be 3min tests.
Click to expand...

Using the same cuvette with mixed reagents over all four tests will yield inaccurate results as reagents continue to react over time.

From the HI774 manual:

C562E153-890D-4AEA-A883-281655C1D884.jpeg
 
The results are more consistent with new regents and dedicate cuvettes were used for each tests.
It took a lilttle longer to mix the regent on the 3rd and 4th test and that could be the reason why last two tests were incosistent.
I will try this again a couple of days later and, this time, I will mix the regent for 1min for all tests.

1664225655032.png
 
Last edited:
After work, I performed 3 tests today with a dedicated regent for each test.
Has anyone tried this?

Test method: Shaked vigorously 50 times and waited for the microbubble to disappear. Same cuvette direction. Cleared with a soft dry towel.
The result: Still getting inconsistent results as I got a 0.04 ppm difference between the 1st and 3rd tests.
My plan: I will switch to HI713 (from HI774) when I run out of the regents.

1665122743455.png
 
Darkxerox said:
Those look perfectly within variability of the assay. It's +/- 0.02 of reading so if your reading is 0.04 then you can see anywhere between 0.02-0.06. I wouldn't worry.
Click to expand...
I think it is good enough to keep a healthy reef. Just feel slightly uncomfortable using this in the long run. :)
 
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