Changes in Salifert Potassium test kit?

[David S]

Hi fellow reefers,

As I have dosed Potassium in my reef tank for a number of years, I found that the best test kit for testing K is the Salifert kit.
So when I began sending ICP samples in, I was naturally curious how my Salifert results measured up.
I found that on a consistent basis the ICP results would measure approximately 20 PPM higher.
This was a good thing due to the consistency.
This trend persisted over a number of years, Salifert test kits, and regardless of the ICP service I used.

Now up until this past June, I had not submitted an ICP test for the better part of a year.
The results from that June submission indicated that my Potassium was 30 PPM lower than the Salifert result.
I thought this might have been a one time aberration, possibly due to an error on my part.
But I have since submitted four more samples for ICP testing and they have all come back ~30 PPM lower than the Salifert result.
I should also mention that I used two ICP companies for the five tests.
I also have two Salifert kits; one is near expiration and the other is good until 2022.
They give identical results.
Again, the fact that the discrepancies between the Salifert and ICP tests have been consistent, is a good thing.
I feel pretty confident, for example, that if my Salifert result indicates 420 ppm, the ICP result will be in the 390 range.

Of course now my Salifert reading is 30 PPM higher when it used to be 20 PPM lower as per ICP.

I was wondering if anyone has experienced a similar shift in comparing the ICP result with Salifert's.
Is it possible Salifert changed their reagents, at some point?

 

[susan ingram]

Hi fellow reefers,

As I have dosed Potassium in my reef tank for a number of years, I found that the best test kit for testing K is the Salifert kit.
So when I began sending ICP samples in, I was naturally curious how my Salifert results measured up.
I found that on a consistent basis the ICP results would measure approximately 20 PPM higher.
This was a good thing due to the consistency.
This trend persisted over a number of years, Salifert test kits, and regardless of the ICP service I used.

Now up until this past June, I had not submitted an ICP test for the better part of a year.
The results from that June submission indicated that my Potassium was 30 PPM lower than the Salifert result.
I thought this might have been a one time aberration, possibly due to an error on my part.
But I have since submitted four more samples for ICP testing and they have all come back ~30 PPM lower than the Salifert result.
I should also mention that I used two ICP companies for the five tests.
I also have two Salifert kits; one is near expiration and the other is good until 2022.
They give identical results.
Again, the fact that the discrepancies between the Salifert and ICP tests have been consistent, is a good thing.
I feel pretty confident, for example, that if my Salifert result indicates 420 ppm, the ICP result will be in the 390 range.

Of course now my Salifert reading is 30 PPM higher when it used to be 20 PPM lower as per ICP.

I was wondering if anyone has experienced a similar shift in comparing the ICP result with Salifert's.
Is it possible Salifert changed their reagents, at some point?

Great question!!! BUMP!!!

 

[David S]

My suggestion to check every test kit by diy reference solution: KCl, osmos water and high precision micro scales.

Could you expand on that?

 

[David S]

Actually, I discovered the discrepancy in readings.
Rather than the Salifert test changing, the different readings were due to the changing of salts.
For years I had been using Instant Ocean and then Tropic Marin Pro. ICP results for either salt gave me consistent K readings.
I subsequently switched to Fritz salt and the low K readings began then.
I've since moved back to TM Pro and my Potassium readings have come back up, both in the Salifert and ICP tests.
Apparently, Fritz's salt is deficient in K.

 

[piranhaman00]

Could you expand on that?

They are saying make a standard solution using potassium chloride. Test with the test kit to see how far off it is. No need to ICP every time to check accuracy.

 

[David S]

They are saying make a standard solution using potassium chloride. Test with the test kit to see how far off it is. No need to ICP every time to check accuracy.

Got that part.
What I don't get is how much KCL am I mixing with how much RODI and what result am I referencing it to?

 

[piranhaman00]

Got that part.
What I don't get is how much KCL am I mixing with how much RODI and what result am I referencing it to?

You will need a high precision mg scale to do this properly. The Gemeni 20 on amazon is a good bet if you dont have lab equipment.

The below math is for a 400ppm Potassium solution using potassium chloride. The idea is create this solution then test with the test kit, it should be 400ppm. Whatever it is off by is the error in the test kit. No need for ICP.

 

[David S]

You will need a high precision mg scale to do this properly. The Gemeni 20 on amazon is a good bet if you dont have lab equipment.

The below math is for a 400ppm Potassium solution using potassium chloride. The idea is create this solution then test with the test kit, it should be 400ppm. Whatever it is off by is the error in the test kit. No need for ICP.

Thanks for the tip about the scale.
So let me see if I have this right:
Does it come down to me measuring out .763 g of KCL powder and then mixing it with 1 liter of RODI to get my 400ppm solution?

 

[piranhaman00]

Thanks for the tip about the scale.
So let me see if I have this right:
Does it come down to me measuring out .763 g of KCL powder and then mixing it with 1 liter of RODI to get my 400ppm solution?

Yes 0.763g (763mg) of KCL in 1 L of rodi will produce a solution that is 400ppm K. Test this solution with a test kit.

I just realized though that the test kit will have to be able to work in freshwater. Not sure how that will affect the test.

 

[David S]

Yes 0.763g (763mg) of KCL in 1 L of rodi will produce a solution that is 400ppm K. Test this solution with a test kit.

I just realized though that the test kit will have to be able to work in freshwater. Not sure how that will affect the test.

Hmm..
Not sure, but it is described as Potassium REEF test.
That sort of implies saltwater.
Something only Habib knows for sure.
In any event, I'll get the scale (sooner or later).
It would be no big deal, then, to try it.
One final question:
Since I wouldn't want to make 1 litre of reference solution and the scale is for very small quantities can I add, for example, 0.19075g to 0.25 litre of RODI for my reference?

 

[piranhaman00]

Yes its made for reef but there are test kits that work for both.

Yes your 1/4 scale would work just fine.

 

[Randy Holmes-Farley Verified Community Expert]

As to the standard, I do not know if the Salifert test will read potassium correctly in fresh water. It might.

 

[Habib(Salifert)]

David asked me to chime in. The Salifert Potassium Reef Test will not read correctly with freshwater. We have a different one for freshwater, using different recipes and a range to 40 ppm.

For future reference purposes one could take water change water, measure it and store say a litre or so in clean plastic soda water bottle. Keeping the cap tightened properly is important to avoid evaporation. In case of an unexpected result that water sample can be measured to see if a consistent result is obtained. Not only suitable for potassium but also salinity, magnesium and possibly calcium if the alkalinity is not too high to force calcium carbonate precipitation. I would not trust it as an alkalinity "reference point".

 

[Randy Holmes-Farley Verified Community Expert]

Thanks, Habib!

 

[David S]

David asked me to chime in. The Salifert Potassium Reef Test will not read correctly with freshwater. We have a different one for freshwater, using different recipes and a range to 40 ppm.

For future reference purposes one could take water change water, measure it and store say a litre or so in clean plastic soda water bottle. Keeping the cap tightened properly is important to avoid evaporation. In case of an unexpected result that water sample can be measured to see if a consistent result is obtained. Not only suitable for potassium but also salinity, magnesium and possibly calcium if the alkalinity is not too high to force calcium carbonate precipitation. I would not trust it as an alkalinity "reference point".

You beat me to it Randy, but thanks Habib