Hanna Phosphorus (HI774) differs greatly from ICP results?

[jfoahs04]

I’ve been fallow for the last 1.5 months and during that time, I’ve battled high phosphates due to overfeeding (still have inverts and coral). I test with the Hanna Phosphate ULR (HI774) which reads in PPM. In the two weeks after going fallow, my P04 jumped from 0.04 to 0.33. I had some RTN on a few acros and generally unhappy coral. I’ve since cut back on feeding and added Chemi Pure Blue (I generally just use Activated Carbon) and am slowly lowering the phosphate numbers (tested at .22 yesterday).

I got ICP results back yesterday and while just about everything else was as expected, my phosphate numbers were less than half of what I’m getting on the Hanna at .101. I would anticipate some discrepancy as the chemistry could change a little during the time between collection and testing, but that’s pretty significant. Anyone have experience with this?

I’m leaning toward continuing to use the Hanna to inform my approach, but I also don’t want to zero out my phosphate if the ICP was more accurate. Should I pick up another test kit? Open to thoughts and suggestions.

 

[blaxsun]

Yesterday I tested my phosphates. My Nyos kit indicated 0.05ppm and my first Hanna ULR test indicated 0.12ppm, so I ran two more Hanna tests and got 0.14ppm and 0.10ppm. Same water sample - same batch of reagents.

Which is more accurate? Honestly, the Nyos. While I might be one color circle off (0.075ppm) in determining the result, there's no way it was 0.1ppm or higher (the tint was teal green and not pale blue).

So myself, I think the Hanna is testing between +0.025ppm and +0.05ppm high. That might sound like a lot, but I'm looking at this on a scale of 0.0-2.0ppm - so this is only 2.5-5% higher. Bubbles, fingerprints and tube orientation can all apparently skew the results.

 

[Dan_P]

I’ve been fallow for the last 1.5 months and during that time, I’ve battled high phosphates due to overfeeding (still have inverts and coral). I test with the Hanna Phosphate ULR (HI774) which reads in PPM. In the two weeks after going fallow, my P04 jumped from 0.04 to 0.33. I had some RTN on a few acros and generally unhappy coral. I’ve since cut back on feeding and added Chemi Pure Blue (I generally just use Activated Carbon) and am slowly lowering the phosphate numbers (tested at .22 yesterday).

I got ICP results back yesterday and while just about everything else was as expected, my phosphate numbers were less than half of what I’m getting on the Hanna at .101. I would anticipate some discrepancy as the chemistry could change a little during the time between collection and testing, but that’s pretty significant. Anyone have experience with this?

I’m leaning toward continuing to use the Hanna to inform my approach, but I also don’t want to zero out my phosphate if the ICP was more accurate. Should I pick up another test kit? Open to thoughts and suggestions.

The ICP PO4 value is unlikely to be more accurate than the Hanna Checker. In fact P is one of the elements that seems to challenge all ICP vendors to get right.

If you are concerned about the value obtained from the Hanna Checker, the only way to test it is to to buy a PO4 standard (NOT the Hanna Checker reference standard).

 

[jfoahs04]

The ICP PO4 value is unlikely to be more accurate than the Hanna Checker. In fact P is one of the elements that seems to challenge all ICP vendors to get right.

If you are concerned about the value obtained from the Hanna Checker, the only way to test it is to to buy a PO4 standard (NOT the Hanna Checker reference standard).

That makes sense, thank you!