Accuracy of Phosphate ICP analysis

[BigJohnny]

Curious because my Hanna ulr phosphorus shows 2-3x more on average than icp. I stopped using it though because my experience with hanna is that they are consistent but accuracy/reagents can vary so it's better for relative measurements, and that assumes perform the test perfectly and clean the tubes perfectly.

Haven't tried another hobby kit recently as I don't and always assumed the ICP was more accurate. Thoughts? Any reason to think the phosphate is being consumed by bacteria in transit or something weird like that, resulting in the much lower reading?

Thanks

 

[Randy Holmes-Farley]

It's possible something happens in transit. How low were the actual numbers?

Triton claims its limit of detection is about 2 ppb P, but I'm not sure how accurate it is at, say 3 ppb.

 

[BigJohnny]

Here is an example, Hanna taken 5 minutes before collecting triton sample:

Hanna- 61 ppb Phosphorous, .19 ppm PO4
Triton- 22 ug/l Phosphorous, .07 mg/l PO4

Usually its a little bit closer but generally about 2x more on Hanna. As you can see not on the low end of their testing, however when i first started the tank the numbers were comparable at around 3ppb/3 ug/l each phosphorous. Sometimes it takes a month+ to get triton results (when you take into account how long it takes me to actually mail the sample). Just trying to figure out how likely it is that the numbers are being cut in half over that time.

I dont really trust the hanna because at one time it consistently said i was at .31-38ppm PO4 (after converting from phosphorous) and I ran 1/4 recommended amount of GFO passively and corals started to pale pretty quickly while still testing .19ppm. It could have been due to the reduction rather than the levels but it wasnt a fast reduction. I also had a low bioload at the time. I pulled the GFO and the corals returned to normal. After GFO it was supposedly reduced to .19ppm PO4 and then i sent a triton test which said .07 PO4. I also found out my alk checker is .9ppm higher than salifert/alkalinity monitor, which i verified via a standard solution. So although my hanna alk has been very consistent, i found it to not be accurate. I therefore assume its very possible the hanna is testing 2x higher than actual.

 

[BigJohnny]

Here is an example, Hanna taken 5 minutes before collecting triton sample:

Hanna- 61 ppb Phosphorous, .19 ppm PO4
Triton- 22 ug/l Phosphorous, .07 mg/l PO4

Usually its a little bit closer but generally about 2x more on Hanna. As you can see not on the low end of their testing, however when i first started the tank the numbers were comparable at around 3ppb/3 ug/l each phosphorous. Sometimes it takes a month+ to get triton results (when you take into account how long it takes me to actually mail the sample). Just trying to figure out how likely it is that the numbers are being cut in half over that time.

I dont really trust the hanna because at one time it consistently said i was at .31-38ppm PO4 (after converting from phosphorous) and I ran 1/4 recommended amount of GFO passively and corals started to pale pretty quickly while still testing .19ppm. It could have been due to the reduction rather than the levels but it wasnt a fast reduction. I also had a low bioload at the time. I pulled the GFO and the corals returned to normal. After GFO it was supposedly reduced to .19ppm PO4 and then i sent a triton test which said .07 PO4. I also found out my alk checker is .9ppm higher than salifert/alkalinity monitor, which i verified via a standard solution. So although my hanna alk has been very consistent, i found it to not be accurate. I therefore assume its very possible the hanna is testing 2x higher than actual.

.9 dkh for the alk checker not .9 ppm sorry

 

[Dennis Cartier]

I noticed the same thing with my Triton results. The PO4 reading was 1/2 of what my Hanna ULR checker was measuring. I was not sure if Triton was under measuring the phosphate, or the Hanna was over estimating the reading. Now that you are reporting the same thing, I am sure that one of them is off. Sadly I am no further ahead on being able to say which one is correct. I am leaning towards Triton being the correct reading.

Dennis

 

[Randy Holmes-Farley]

I'd personally lean toward Triton too, but I have no proof.

If Triton was higher than might be organic phosphate being read too, but this way around, that can't be the explanation.

 

[2una]

I gave up bothering to trust & use the Hanna ulr cos of its lies. My Ati icp po4 results are pretty much the same as i get from either redsea po4 & or Elos high res po4 kits.

.9 dkh for the alk checker not .9 ppm sorry

I also find the same,it reads almost 1 dkh high

 

[GoVols]

I gave up bothering to trust & use the Hanna ulr cos of its lies. My Ati icp po4 results are pretty much the same as i get from either redsea po4 & or Elos high res po4 kits.

2una,
Thanks for the info.

I was using the ULR checker, but when I bought new reagent powers last summer, my phos. read zero and the rest of the year it came in at .05 ppm with the old reagent batch.

I just don't trust their refills from one batch to the other with the ULR checker.

(lol)
I guess, I'll try out the Red Sea kit.

 

[2una]

2una,
Thanks for the info.

I was using the ULR checker, but when I bought new reagent powers last summer, my phos. read zero and the rest of the year it came in at .05 ppm with the old reagent batch.

I just don't trust their refills from one batch to the other with the ULR checker.

(lol)
I guess, I'll try out the Red Sea kit.

Hi Freddie - yeah doesn't surprise me that, The Elos has been solid - the Redsea works well but i'm often double checking it,I like their No3 & Po4 kits but confirm with something else regularly to make sure its not gone out of whack.The newer black box ones i haven't had turn bad on me.

 

[GoVols]

Hi Freddie - yeah doesn't surprise me that, The Elos has been solid - the Redsea works well but i'm often double checking it,I like their No3 & Po4 kits but confirm with something else regularly to make sure its not gone out of whack.The newer black box ones i haven't had turn bad on me.

I'll give Elos ago, then.

Right now, when I need to clean the glass more often... (lol) it's time to re-charge the GFO... ;Wacky

 

[rkpetersen]

I just had the exact opposite experience with phosphorus.

Fairly new tank, not much livestock. 3 weeks ago, Hanna ULR Phosphorus checker read 0 ppb. Triton sample obtained at the same time, came back as 10 ppb.

In general, I've been pretty happy with this checker on my older tank. It's compared reasonably well with ICP testing on many occasions. I've tried many other kits and they all had problems or issues of one kind or another. That tank is a Red Sea Reefer and I started with all Red Sea test products, but have moved away from almost all of them. I seem to recall their phosphate test was insensitive and inaccurate at the low end.

 

[BigJohnny]

I'd personally lean toward Triton too, but I have no proof.

If Triton was higher than might be organic phosphate being read too, but this way around, that can't be the explanation.

Yes I have been trusting the triton but because of the time delay between taking the sample and the actual test (not to mention the possible changes in environmental conditions along the way) I am curious if that is part of what's going on.

 

[BigJohnny]

I gave up bothering to trust & use the Hanna ulr cos of its lies. My Ati icp po4 results are pretty much the same as i get from either redsea po4 & or Elos high res po4 kits.



I also find the same,it reads almost 1 dkh high

Which do you prefer, the redsea or elos? I'd like to try another hobby kit. Also which is easier to interpret the results?

 

[BigJohnny]

I just had the exact opposite experience with phosphorus.

Fairly new tank, not much livestock. 3 weeks ago, Hanna ULR Phosphorus checker read 0 ppb. Triton sample obtained at the same time, came back as 10 ppb.

In general, I've been pretty happy with this checker on my older tank. It's compared reasonably well with ICP testing on many occasions. I've tried many other kits and they all had problems or issues of one kind or another. That tank is a Red Sea Reefer and I started with all Red Sea test products, but have moved away from almost all of them. I seem to recall their phosphate test was insensitive and inaccurate at the low end.

Interesting. After hearing that recommendation and researching it looks like the elos high resolution is considered a good one. I don't even really care about my phosphate levels but it would be nice to be able to see where they are at occasionally and notice if the tank looks better or worse.

 

[2una]

Which do you prefer, the redsea or elos? I'd like to try another hobby kit. Also which is easier to interpret the results?

I like both about equally to use but i have an historic mistrust of any redsea kit.
The Redsea test is 2 sets of reagent drops,2nd reagent add is via a bit stupid design small plastic dropper - i'm not fond of that but it works.Uses 2 x 17ml water sample.
The Elos is drops of 1 & powder scoop of another. uses 2 x 20ml samples,they use a tall/narrow design vial - these vials have a packer they sit in but you do need to still take some care with them.
Easiest to read will probably depend on your eye - i find them both pretty much the same,you do need to go high & low on the cd or card on both but you can get out an answer pretty comfortably.

 

[Hans-Werner]

If the phosphate concentration of the ICP-OES is higher than that shown by the checker the explanation may be easy: ICP-OES shows total phosphate while wet chemical tests show reactive phosphate and the difference may very well be threefold or more. If it is vice versa it is much more difficult to explain. Phosphate may be adsorbed to the bottles during transportation. We had high losses of phosphate to plastic bottles overnight at low concentrations. I think acidification of the sample is meant to prevent adsorption to bottles.

 

[tastyfish]

Interesting. My Hanna ULR has given pretty consistent results in line with the ICP-OES results. There is a margin for error on both, but I would probably trust the ICP more than a home test kit?

I have a very regimented and by the book proceedure with the ULR tester. It must be followed, otherwise I have experienced inconsistent results or those which are far higher than reality.

 

[BigJohnny]

If the phosphate concentration of the ICP-OES is higher than that shown by the checker the explanation may be easy: ICP-OES shows total phosphate while wet chemical tests show reactive phosphate and the difference may very well be threefold or more. If it is vice versa it is much more difficult to explain. Phosphate may be adsorbed to the bottles during transportation. We had high losses of phosphate to plastic bottles overnight at low concentrations. I think acidification of the sample is meant to prevent adsorption to bottles.

Hans-Werner, the man, the myth, the legend! thanks for posting. Interesting I never considered the possibility that the containers themselves could be absorbing the phosphate. If you were seeing losses over night then it seems possible that 30 days in those same containers could absorb much more. That of course assumes that the containers wouldnt absorb everything within the first 24hrs and that they have the ability to absorb much more than you saw, which i have no idea.

Thoughts?

 

[BigJohnny]

Interesting. My Hanna ULR has given pretty consistent results in line with the ICP-OES results. There is a margin for error on both, but I would probably trust the ICP more than a home test kit?

I have a very regimented and by the book proceedure with the ULR tester. It must be followed, otherwise I have experienced inconsistent results or those which are far higher than reality.

Yea I am leaning towards ICP but I do believe there is a definite possibility some is being lossed or fixed or something during transit. For sure on the Hannas, I am very careful with the tests as well. I wear nitrile gloves at all times and wipe the cuvette clean several times during the testing process with a microfiber cloth. I also clean them inside and out before and after every test. Well, i used to, i dont use them anymore.

 

[Mortie31]

I also get triton about 50% of my hanna ulr reading, and I index my viles and follow the Hanna instructions to the letter.