Thoughts on Hannah PO4 meter having inconsistent but close readings?

[BOMPH]

So I have been doing my PO4 test every other day to every 3 days or so. I have been getting very inconsistent but close readings. I perform 3 tests consecutively each time using the same vial and reagents from the same lot, rinsing and cleaning between each test, and I will get 0.00, 0.03, 0.05, basically any number between 0.00 and 0.05 ( one time I did get 0.10 ). Thoughts on this? SHould I just average the values and say 'Thats my reading for today'? Could this be indicative that my meter is going bad? ( this IS a replacement of one that died about 6 months ago ).

Another question: I cant seem to get all the reagent to dissolve in the 2-3 minutes i have once i am in 'C2' mode before the auto shut off kicks in.... So, there are particles of the reagent in the vial when I hold the button so it goes into the 3 minute countdown. Normal?

EDIT: Thought I should add that I pulled a GFO reactor about 3 weeks ago and have been dosing NoPox during that time, PO4 inconsistency reading has been happening since before the change, NO3 is sitting at just barely detectable on a Red Sea Pro Kit ( ie: just a tinge of color, not deep enough to be the .25 reading on the wheel ).

 

[bif24701]

I have not had any problems like that with my ULR Hanna.

I do the following:
Rise vial in tank water several times, run the base line test, add reagent, shake 60 seconds, put in Hanna Checker, hold button for 3:00 timer. Auto tests after timer expires. Each week, each test within .01 phosphorous. High accuracy IMHO.

 

[Randy Holmes-Farley Verified Community Expert]

So I have been doing my PO4 test every other day to every 3 days or so. I have been getting very inconsistent but close readings. I perform 3 tests consecutively each time using the same vial and reagents from the same lot, rinsing and cleaning between each test, and I will get 0.00, 0.03, 0.05, basically any number between 0.00 and 0.05 ( one time I did get 0.10 ). Thoughts on this? SHould I just average the values and say 'Thats my reading for today'? Could this be indicative that my meter is going bad? ( this IS a replacement of one that died about 6 months ago ).
.

Which Hanna?

That's exactly what would be expected from the 713 since it has an uncertainty of +/- 0.04 ppm.

 

[BOMPH]

Which Hanna?

That's exactly what would be expected from the 713 since it has an uncertainty of +/- 0.04 ppm.

Yes HI 713. Is there a 'better' model?

 

[Randy Holmes-Farley Verified Community Expert]

The Hi736 can read somewhat lower and has somewhat tighter error bars, but I've not personally used either one.

 

[BOMPH]

Ahh the joy of this hobby... someone is always building a better mousetrap. Thank you!

 

[bif24701]

Ahh the joy of this hobby... someone is always building a better mousetrap. Thank you!

If you have the 713 I don't see major reason to purchase another to be completely honest. Are you concerned for high phosphates and use products that may quickly lower phosphate like Phosphate RX? Using a GFO calculator to determine the amount I would say it's safe to use without strict testing.