Developing a potassium test, salifert-style (or alternative)

[David S]

Sending out an ICP test in a little while.
As per usual, I test routine parameters as a means of comparison.
Test for the Salifert Potassium kit came in @ ~ 420 - 430 PPM.

BTW I received a notification from Chewy indicating that they have the Salifert K test as well.

 

[JCOLE]

FYI, I just received three of the new kits. They do have a smaller, clearer bottle compared to the old one. I tested both the old kit and the new kit, and I received the same reading.

 

[David S]

Sending out an ICP test in a little while.
As per usual, I test routine parameters as a means of comparison.
Test for the Salifert Potassium kit came in @ ~ 420 - 430 PPM.

BTW I received a notification from Chewy indicating that they have the Salifert K test as well.

Ok
I received the results of my ICP test.
It was done by Triton.
Overall, the elements were not much different than other recent ICP submissions.
There was one discrepancy, though.
Ironically, it was Potassium!
The ICP test indicated a concentration of 526 PPM. That is about 100 PPM above what the Salifert test showed.
Quite frankly, I am skeptical about Triton's results. Not only does it leave the normally reliable Salifert test in question, it is an historically high ICP result for this element- and I have done many ICP tests (current Salifert reading is 450 PPM).
I intend to do another ICP with Fauna Marin in a few weeks and I'll make another comparison.

 

[Rick Mathew]

Ok
I received the results of my ICP test.
It was done by Triton.
Overall, the elements were not much different than other recent ICP submissions.
There was one discrepancy, though.
Ironically, it was Potassium!
The ICP test indicated a concentration of 526 PPM. That is about 100 PPM above what the Salifert test showed.
Quite frankly, I am skeptical about Triton's results. Not only does it leave the normally reliable Salifert test in question, it is an historically high ICP result for this element- and I have done many ICP tests (current Salifert reading is 450 PPM).
I intend to do another ICP with Fauna Marin in a few weeks and I'll make another comparison.

Remind me again are you dosing potassium regularly?

 

[David S]

Remind me again are you dosing potassium regularly?

Yes
I've been dosing (Potassium Chloride) for years.
However, I have reduced the amount, over the past year, to about 0.2 ml daily, as ICP tests indicated concentrations in the 450 + range.
I do dissolve a large amount of KCL in RODI water.
I just lowered the dose to 0.1
We'll see what happens.

 

[David S]

Yes
I've been dosing (Potassium Chloride) for years.
However, I have reduced the amount, over the past year, to about 0.2 ml daily, as ICP tests indicated concentrations in the 450 + range.
I do dissolve a large amount of KCL in RODI water.
I just lowered the dose to 0.1
We'll see what happens.

Thinking about it, in retrospect, I have increased the concentration of KCL in my solution, considerably, over the years.
Might be better served lowering the concentration, somewhat.

 

[Rick Mathew]

Thinking about it, in retrospect, I have increased the concentration of KCL in my solution, considerably, over the years.
Might be better served lowering the concentration, somewhat.

On the sample comparison you did were the ICP samples and your home test samples taken at the same time? Also are you hand dosing or using a doser?

 

[David S]

On the sample comparison you did were the ICP samples and your home test samples taken at the same time? Also are you hand dosing or using a doser?

Exact same time.
I am using a Kamoer X1, daily, to dose.
BTW, I have always checked my K with Salifert before sending out ICP's - that is until I ran out.
I can't recall ever getting an exact match, but usually the results are within 20 - 40 PPM of each other.
While I'm not that anal to go through all my previous ICP results for Potassium, I'm pretty sure this is the highest reading; which I don't buy.
I'll get a better idea with the next test.
Sure hope I'm right. Otherwise, I may have to chuck the Salifert, or if the discrepancy is consistent, factor in an adjustment.

 

[David S]

Hi All
Received results from latest ICP from Fauna Marin.
Potassium was 448 PPM. The Salifert test indicated a level between 430 - 440 PPM.
BTW most, if not all of the time, my Salifert readings for K, now and in the past l, ran slightly lower than ICP.
I am concluding that the current Salifert test is reasonably accurate (similar to past readings) and the Triton reading of 526 PPM was an outlier.
Having said that I notice that my Potassium is unusually high, considering I have stopped dosing it.
I do about 10% weekly water changes with ESV salt.
I occasionally dose Fuel, which to my knowledge does not have Potassium.
I also dose Seltzer water, during the day, as my PH runs high. While it does contain some sodium, it "is not a significant source of Potassium".
Any ideas?

 

[taricha]

Hi All
Received results from latest ICP from Fauna Marin.
Potassium was 448 PPM. The Salifert test indicated a level between 430 - 440 PPM.

That's about as good as agreement can get across methods like that.
That's also about where mine runs. Were you hoping it was lower?

 

[David S]

That's about as good as agreement can get across methods like that.
That's also about where mine runs. Were you hoping it was lower?

I agree.
I'd like it a bit lower, say 400 - 420 range.
What concerns me is for years, I've been dosing KCL to keep my Potassium up. Been doing it for years.
Suddenly, I have fairly high readings with no dosing.
Wondering what's causing it.
I will ease off on the Fuel to see if that is the cause.

 

[darknectar]

the variability day to day will be less than 10%. There seems to be some lot-to lot issues with Red Sea reagent that is making us look into other sources for tetraphenylborate for the test.


Not in the same way as the PO4 checkers we've used. It measures PO4 a different way, so you'll need your own calibration curve....

Method

adaptation of the Standard Methods for the Examination of Water and Wastewater, 18th edition, Amino Acid method

It uses the amino acid method instead of the ascorbic acid method that the other PO4 checkers do, so you can't expect the absorbance scale of that high range checker to be similar to the other PO4 checkers.

(I think the following is correct) ammonium will bind in place of K to the TPB and precipitate, so 1 mole of ammonium will get counted like 1 mole of K, so 1-4ppm of ammonium will get counted as ~ 2.2x that much K in ppm.


I have no reason to think that lack of NaCl will change the way the precipitation seems to work. I haven't run the test on K in a freshwater sample.



Due to the Red Sea issues I mentioned, (weird lot-to lot performance and squirrelly answers about future availability) We're currently looking at the exaqua reagent (5-10% TPB) because it's intended to be used the way we want to use it (turbidity) and it's cheap.

Hach sells pure Na-TPB and it's more than you'll ever need, but expensive.
https://www.hach.com/p-potassium-3-reagent-powder-pillows-pk100/1432399

Hi @taricha

I've been using this turbidity method now for 6 months and using the Red Sea Reagent B. I think it works really well.

I'm about to run out and would like to make my own.

Based on the msds from Red Sea, it says 1-5% sodium tetraphenylborate and 25%-50% Ethylene glycol. I will use distilled water.
I'm going to buy sodium tetraphenylborate from here.

Sodium tetraphenylborate, 99% 5 g | Buy Online | Thermo Scientific Chemicals | thermofisher.com

Sodium tetraphenylborate, 99%. Sodium tetraphenylborate is used as a precipitating reagent for potassium and as a protecting agent to protect amino acids. It is used in the preparation of N-acylammonium salts. It finds application. Available in 5 g

www.thermofisher.com

Any ideas on what % of sodium tetraphenylborate and ethylene glycol I should use? Does it matter water order I mix them?

 

[taricha]

Hi @taricha

I've been using this turbidity method now for 6 months and using the Red Sea Reagent B. I think it works really well.

I'm about to run out and would like to make my own.

Based on the msds from Red Sea, it says 1-5% sodium tetraphenylborate and 25%-50% Ethylene glycol. I will use distilled water.
I'm going to buy sodium tetraphenylborate from here.

Sodium tetraphenylborate, 99% 5 g | Buy Online | Thermo Scientific Chemicals | thermofisher.com

Sodium tetraphenylborate, 99%. Sodium tetraphenylborate is used as a precipitating reagent for potassium and as a protecting agent to protect amino acids. It is used in the preparation of N-acylammonium salts. It finds application. Available in 5 g

www.thermofisher.com

Any ideas on what % of sodium tetraphenylborate and ethylene glycol I should use? Does it matter water order I mix them?

Sorry I missed this. I'll look back through my notes and see if I can answer.

 

[taricha]

I've been using this turbidity method now for 6 months and using the Red Sea Reagent B. I think it works really well.

I'm about to run out and would like to make my own.

Based on the msds from Red Sea, it says 1-5% sodium tetraphenylborate and 25%-50% Ethylene glycol. I will use distilled water.
I'm going to buy sodium tetraphenylborate from here.

Sodium tetraphenylborate, 99% 5 g | Buy Online | Thermo Scientific Chemicals | thermofisher.com

Sodium tetraphenylborate, 99%. Sodium tetraphenylborate is used as a precipitating reagent for potassium and as a protecting agent to protect amino acids. It is used in the preparation of N-acylammonium salts. It finds application. Available in 5 g

www.thermofisher.com

Any ideas on what % of sodium tetraphenylborate and ethylene glycol I should use? Does it matter water order I mix them?

OK. Red Sea directions for the back-titration imply that 0.500mL of Reagent B (TPB solution) reacts totally (1:1) with all the K in 2.00 mL of 470 ppm water. You might check your latest red sea instruction card to ensure that is still the ratios of reagent B and sample water, and they didn't change the kit.

the above calculation indicates you could make the Red Sea strength reagent B with 16.45 grams of sodium tetraphenylborate per 1L or water or more conveniently, 0.1645grams per 10mL.
(this 1.645% is consistent with the 1-5% range on the MSDS.)

[edit: for turbidity, we are in excess on TPB - like 6.5 to 1 mole ratio vs K in the sample, so it's not 1:1 like titration and the exact concentration isn't as crucial as it is for the standard back-titration method that Red Sea and others are using.]

As for the ethylene glycol, I think it's a stabilizer (the TPB solution can be unstable over extended time) with no real effect on the turbidity test. So I'd go with the low 25% in the MSDS and keep the batches of solution small, and not keep them more than a month. Easily done since you are DIY-ing solution from a bunch of stable bulk solid.

(You should sanity-check the resulting solution results vs actual red sea reagent B to see if I botched anything badly.)

 

[reefdev Verified Admin]

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