Help with measuring phosphates.

[nick0206]

Hello.
I launched a new tank half a year ago. Although I still have a dino problem, all lps and sps corals are doing fine.
Since the aquarium is still not stable, I need to control the levels of nitrates and phosphates.
I measure phosphates with Hanna photometers. I have 3 of them.
1, Normal - 713
2, For ultra low levels 774
3, Phosphorus measurement - 736
The problem was that 713 always shows 0.00 for me, and 774 is a very high level.
All reagents are in order, another year is good.
I was advised to calculate the level of phosphate by phosphorus, i.e. I measure the level of phosphorus and according to the table given on the Hanna site determine the level of phosphates.
For example today
713 - 0.00
774 - 0.11
736 - phosphorus - 11, and according to the table it is 0.034 phosphates.
Could anyone explain such a difference and which device should be trusted more?
PS 1 I never touch cuvettes with my fingers.
PS 2 I usually shake it very vigorously, which allows the powder to dissolve quickly, then open the cap for a minute to let the air out. Usually no bubbles remain.
Thank you in advance

 

[blaxsun]

I like my Nyos test kit for phosphates.

 

[T-J]

1. Weigh the 10ml of tank water. Don't trust the line on the cuvette.
2. Make sure you're getting all of the powder into the cuvette. With such small amounts, if you're missing just a little, it can skew the results.
3. Cap and shake the vial for 2 minutes. No need to open the cap and let it breathe.
4. Press and hold the button on the checker to start the countdown. DO NOT simply press the button and let go, giving you an instant result.
5. Take a sample to an LFS or send in a sample for ICP testing to see how they compare to your results.

 

[dwest]

Hello.
I launched a new tank half a year ago. Although I still have a dino problem, all lps and sps corals are doing fine.
Since the aquarium is still not stable, I need to control the levels of nitrates and phosphates.
I measure phosphates with Hanna photometers. I have 3 of them.
1, Normal - 713
2, For ultra low levels 774
3, Phosphorus measurement - 736
The problem was that 713 always shows 0.00 for me, and 774 is a very high level.
All reagents are in order, another year is good.
I was advised to calculate the level of phosphate by phosphorus, i.e. I measure the level of phosphorus and according to the table given on the Hanna site determine the level of phosphates.
For example today
713 - 0.00
774 - 0.11
736 - phosphorus - 11, and according to the table it is 0.034 phosphates.
Could anyone explain such a difference and which device should be trusted more?
PS 1 I never touch cuvettes with my fingers.
PS 2 I usually shake it very vigorously, which allows the powder to dissolve quickly, then open the cap for a minute to let the air out. Usually no bubbles remain.
Thank you in advance

That’s a tough problem. I would talk to Hanna. I use the ULR phosphorus unit. It seems to give me repeatable results that makes sense. But I’ve never compared them to others.

Thinking more…Your 11 value with the ULR is very low (compared to mine). I am wondering if you are in such a low range that all of the values are within testing limits.

 

[nick0206]

That’s a tough problem. I would talk to Hanna. I use the ULR phosphorus unit. It seems to give me repeatable results that makes sense. But I’ve never compared them to others.

Thinking more…Your 11 value with the ULR is very low (compared to mine). I am wondering if you are in such a low range that all of the values are within testing limits.

Thanks for the quick response.
What do you mean 11 is low? If phosphorus, then yes, probably, but if phosphate is 0.11, then for me this is a lot.
Since the system is new, I try to keep phosphates at 0.03-0.06 and nitrates at 3-6.
The only thing that worries me is the readings of 774. Considering that 713 gives an error of 0.04, then 0.00 and 0.034 are comparable, but 0.11 is too much.
Moreover, my LFS contains calibration fluid for 774, and the test showed that my device is working correct. The only thing I think is that something is wrong with the reagents themselves.

 

[Randy Holmes-Farley]

Don't forget that all of these have uncertainties, even when functioning and used perfectly.

According to Hanna:

The 713 has error of +/- 0.04 ppm
The 774 has uncertainty of +/- 0.02 ppm
The 736 has uncertainty of +/- 5 ppb phosphorus = +/- 0.015 ppm phosphate

Thus, a true value of 0.05 ppm is not far off of all of your readings, given the uncertainties.