Hanna Phosphorus Test Turning Navy Blue - help

[jjencek]

I have been using the Hanna Checker Phosphotus ULR for some time now.

My results are pretty consistent between 0 to 5 ppb (0.01533 ppm phosphate).

About two weeks ago it was close to zero.

When I measured it today, the solution turned navy blue as soon as I added the reagent to it. Of course the tester went over the scale.

I have never seen it before - anybody has an explanation?

 

[jjencek]

I have additional information ...

I purchased SALIFERT Phosphate test kit to verify the Hanna results. I know SALIFERT is not that accurate in low values, but I see very little color change - indicating 0-0.03 ppm.

That really does not make sense. Hanna checker HI 736 indicates above the limit of the checker. That would be, after conversion, above 0.6132 ppm.

 

[mcgyvr]

And did you try a second test using the Hanna kit after your first failure?
Did it turn dark blue?

 

[jjencek]

And did you try a second test using the Hanna kit after your first failure?
Did it turn dark blue?

Yes, I tried a second test and a third one next day. I even switched test tubes, just in case they were contaminated.

Same result.

 

[bertoni]

Hmm, that sounds like bad reagents to me, or maybe the vials are contaminated. I might try cleaning them with a bit of vinegar, but I suspect that the reagents are bad.

 

[jjencek]

Hmm, that sounds like bad reagents to me, or maybe the vials are contaminated. I might try cleaning them with a bit of vinegar, but I suspect that the reagents are bad.

These are the same batch of reagents I used with "normal" results. I also cleaned the vials (RODI water only). I even used three different vials.

 

[bertoni]

Well, you could try testing some freshly-mixed saltwater. Maybe it's the tank, but then the Salifert must be wrong.

 

[outssider]

Well, you could try testing some freshly-mixed saltwater. Maybe it's the tank, but then the Salifert must be wrong.

+1 do this ^

If it turned as blue as you say and the reagents are good you have unbelievably high po4.....I hope it's the reagents :sad2:

 

[jjencek]

So I have been playing with the tester until I ran out of reagents.

Just mixing Red Sea salt in RODI does have some phosphate in it. I measured 0.073584 ppm.

But here is the weird stuff ... I tested the DT again and the blue color is nowhere to be seen. The results are back to normal - about 0.012264 ppm.

So the temporary issue is gone.

I do have one theory that I will verify when I get more reagents. I have two Hanna checkers, one for phosphates and the other one for copper. I mixed up all the vials and don't know which one I used with each tester. MAYBE the copper reagent traces react with the phosphorus reagent.

 

[Vinny Kreyling]

I would suggest @ a minimum to clean all the vials with vinegar & rinse with RO water before drying.

 

[bertoni]

I agree with giving the vials a good cleaning. Vinegar is what I'd use.