# Potassium test?



## MichaelJ (19 Apr 2021)

I recently started to mix tap water and RO for my weekly WC. In the past I did pure remineralized RO water partly because my household water-softener used Sodium Chloride for softening. About a month ago I switched over to using Potassium Chloride, and all seems to be good at this point, but I am kind of curious about the residual level of Potassium that ends up in my tanks. Does anyone know a reasonably reliable indicative test kit for Potassium (K)  ? I did see some kits targeted for reef/saltwater tanks, but noting for freshwater tanks.  

Another thing I am wondering about is whether the Potassium Chloride is beneficial to the plants in a comparable way to the soluble potash that is usually found in fertilizers (such as Seachem Potassium) ?

Cheers


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## dw1305 (19 Apr 2021)

Hi all,


MichaelJ said:


> Potassium Chloride is beneficial to the plants in a comparable way to the soluble potash


Yes, exactly the same, nearly all potassium compounds are soluble, and every potassium (K+) ion is the same as every other K+ ion, it doesn't matter which compound it comes from. Plants can only take up nutrients as ions from solution.







MichaelJ said:


> About a month ago I switched over to using Potassium Chloride, and all seems to be good at this point, but I am kind of curious about the residual level of Potassium that ends up in my tanks.


_"All seems good"_ would be take home from that and I wouldn't be too bothered after that, but it will be quite a lot. How much depends on how hard your water is because it is going to swap a calcium ion (Ca++) for two potassium (K+) ions. <"It is "strong acid"  ion exchange">, so the it doesn't effect the anion, you add K2CO3 (2K+ & HCO3-) to the tank, rather than CaCO3.


MichaelJ said:


> Does anyone know a reasonably reliable indicative test kit for Potassium (K) ?


Difficult because of the <"solubility of potassium compounds">. Analytically it is easy via flame photometry, AAS or ICP.  The <"LaMotte test kit is a possibility"> and uses turbidity:


> ........ Sodium tetraphenylboron reacts with potassium to form a white precipitate. The turbidity of the solution is proportional to potassium concentration which is measured in a calibrated tube....



cheers Darrel


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## orxe87 (19 Apr 2021)

I believe the JBL test uses the same method - at least the one I have creates a white precipitate, the turbidity of which is measured in a calibrated tube over a black 'x' on the test chart. I have the JBL reagents but unfortunately I've misplaced the calibrated tube!


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## sparkyweasel (19 Apr 2021)

@dw1305 , would it be easier to to test the untreated tapwater for hardness and calculate the potassium from there?


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## MichaelJ (19 Apr 2021)

@dw1305


dw1305 said:


> Hi all,
> 
> Yes, exactly the same, nearly all potassium compounds are soluble, and every potassium (K+) ion is the same as every other K+ ion, it doesn't matter which compound it comes from. Plants can only take up nutrients as ions from solution.



Thanks Darrel for the clarification!



dw1305 said:


> _"All seems good"_ would be take home from that and I wouldn't be too bothered after that, but it will be quite a lot.


Right. I haven't been able to find any sources that talks about potassium poisoning of livestock or plants either, but I guess there is a limit. At least, I don't have to worry about Potassium deficiency!



dw1305 said:


> How much depends on how hard your water is because it is going to swap a calcium ion (Ca++) for two potassium (K+) ions. <"It is "strong acid"  ion exchange">, so the it doesn't effect the anion, you add K2CO3 (2K+ & HCO3-) to the tank, rather than CaCO3.


The water coming in to the softener is around 20-22 GH and what comes out is essentially "0" GH.



dw1305 said:


> <"LaMotte test kit is a possibility">


Out of general curiosity, I might try the LaMotte test kit, to see what the level is out of the tap. It's a hefty $87 USD + Tax and shipping. 

Cheers
Michael


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## MichaelJ (19 Apr 2021)

sparkyweasel said:


> @dw1305 , would it be easier to to test the untreated tapwater for hardness and calculate the potassium from there?



@sparkyweasel

Of course I never thought of that....  I did a quick search:
I found this pdf on WHOs website - see page 8:
Potassium in drinking-water - WHO | World Health Organizationhttps://www.who.int › potassium-background

My inlet water is 20-22 GH but I do not know the Calcium carbonate contribution to my GH. but if it's say 50% for the sake of argument, my potassium level out of the softener is probably around 160 ppm if I understand this correctly - if so, that would make my 50/50 RO/Tap  potassium level 80 ppm.

Cheers


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## dw1305 (20 Apr 2021)

Hi all, 


sparkyweasel said:


> would it be easier to to test the untreated tapwater for hardness and calculate the potassium from there





MichaelJ said:


> My inlet water is 20-22 GH but I do not know the Calcium carbonate contribution to my GH. but if it's say 50% for the sake of argument, my potassium level out of the softener is probably around 160 ppm if I understand this correctly - if so, that would make my 50/50 RO/Tap potassium level 80 ppm


Yes you could test for dKH ("alkalinity") and work from the assumption that that hardness came entirely from Mg/CaCO3, like @MichaelJ has done.


MichaelJ said:


> I haven't been able to find any sources that talks about potassium poisoning of livestock or plants either, but I guess there is a limit.


There will be, but "pretty high" would be my guess for most plants. For fish it might depend where they came from, but you get water bodies with high potassium levels, like <"Lake Tanganyika">. 


MichaelJ said:


> Out of general curiosity, I might try the LaMotte test kit, to see what the level is out of the tap. It's a hefty $87 USD + Tax and shipping.


LaMotte tests are generally aimed at scientists. Because potassium is so easy to test for in the lab. (using relatively cheap analytical equipment), there would be a limited demand for a test kit you could use in the field, normally you would just take a small volume water sample back to the lab..

cheers Darrel


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## MichaelJ (20 Apr 2021)

dw1305 said:


> Hi all,
> 
> 
> Yes you could test for dKH ("alkalinity") and work from the assumption that that hardness came entirely from Mg/CaCO3, like @MichaelJ has done.



Thanks @dw1305

After this discussion I suppose (and correct me if I am wrong) another way of estimating the contents, is if my potassium Cl softened tap water TDS is around 270 ppm with a KH 10-11 (say that's 180 ppm) and  assuming ALL the remaining TDS is from the potassium (which of course is not the case) the upper bound of the potassium contents of the softened tap would be around 90 ppm ? 
And of course, after being mixed 50/50 with RO water it would drop to 45 ppm.  (realistically more like upper 30ties).

Edit: Actually my Tap/RO mix after remineralization is around 250 ppm (with GH 5 and KH 6 or 198 ppm), which leaves around 50 ppm for everything else, so my upper 30ties guess seems fair.




dw1305 said:


> There will be, but "pretty high" would be my guess for most plants. For fish it might depend where they came from, but you get water bodies with high potassium levels, like <"Lake Tanganyika">.


FWIW After searching around a little more I did see a brief mention at the Barrreport where Barr mentions The only known excess ranges for K+ would be well in excess of 200ppm 

Cheers
Michael


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## ceg4048 (21 Apr 2021)

MichaelJ said:


> FWIW After searching around a little more I did see a brief mention at the Barrreport where Barr mentions The only known excess ranges for K+ would be well in excess of 200ppm


Yeah, exactly. 
Here is a tank dosed weekly at approximately 150ppm K+ (intentionally), with KH greater than 20 (intentionally) and GH greater than 26 (intentionally).
Worrying about Potassium toxicity is a complete waste of energy.
Never worry about NO3/PO4/K, KH/GH, or trace toxicity.
Always worry about CO2. That's where about 95% of your problems will be.





Cheers,


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## MichaelJ (21 Apr 2021)

ceg4048 said:


> Yeah, exactly.
> Here is a tank dosed weekly at approximately 150ppm K+ (intentionally), with KH greater than 20 (intentionally) and GH greater than 26 (intentionally).
> Worrying about Potassium toxicity is a complete waste of energy.



@ceg4048
150 ppm K+  ..Well, that makes it abundantly clear that K+ in excess is not something I should even begin to worry about. And your results speaks for itself...  Actually, I was mostly curious as to how to determine the contents. Again, out of curiosity since both my tanks are doing fine. But always good to be reminded and that high NPK and trace is never an issue... I run both my tanks at fairly high Nitrate and Phosphate levels anyway (and now K I assume).

Thanks as always!


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## jaypeecee (21 Apr 2021)

Hi @MichaelJ



MichaelJ said:


> I haven't been able to find any sources that talks about potassium poisoning of livestock or plants either, but I guess there is a limit.



Somewhere, here on UKAPS, I once made reference to potassium toxicity as I wondered if it had caused the death of my Panda Garras about 18 months ago. I have done several searches for this on UKAPS - to no avail. In the back of my mind, potassium level had reached around 90 ppm. I would recommend pursuing this further for the benefit of your livestock.

JPC


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## MichaelJ (21 Apr 2021)

jaypeecee said:


> Hi @MichaelJ
> 
> 
> 
> ...



Hi @jaypeecee

Thanks for the heads up. I looked around re. toxicity and only found the above mention by Barr myself - and as @ceg4048 pointed out he runs his at 150 ppm ... not sure what livestock he got in there though.
I've been through 5 weekly 40-50% WCs since I switched over to Potassium Chloride in my water softener (doing 50/50 Tap/RO) and I haven't noticed any deterioration of livestock or plant health - actually my plants look better than ever, but that is probably due to a multitude of other factors such as upping the weekly WC from 20% to 40%, better (and simpler) WC water prep routine and better maintenance in general. So I really have absolutely no reason to be worried at this point, but I will definitely keep the K (and other things I've changed) in mind if I notice anything starting to go south.
I dont really do much measuring other than immediately before WC where I measure TDS, KH and GH and a day after where I do the same measurements just to get those data points for comparison and to make sure I don't get too much of a spike week-over-week in TDS which appears to be a good sign of poor maintenance on my part. At least, some of my livestock is considered pretty finicky (Golden Rams, Angles, various tetras including Cardinals).

Cheers,
Michael


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## sparkyweasel (22 Apr 2021)

This may be of interest;
KCl Salmonids

Extract;
"Minimal mortality (one fish) occurred across all KCl exposures. . . .
The single mortality was a Chinook salmon tested at 200 mg/L KCl
at low baseline water conductivity. The mortality occurred at the end
 of the trial, and was noted at the termination of the 96-hour exposure. 
At necropsy, this fish was generally pale, yet there were no gross lesions
noted and no obvious proximate cause of death."


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## MichaelJ (22 Apr 2021)

@sparkyweasel 
Very interesting indeed. Thanks.


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## jaypeecee (24 Apr 2021)

sparkyweasel said:


> This may be of interest;
> KCl Salmonids


Hi @sparkyweasel 

I have a copy of that paper from a while back but I thought I had other papers on this question about potassium toxicity to fish and other aquatic creatures. Alas, I have scoured my collection of papers with no significant success. I am really surprised that there appears to be nothing out there. As well as using _Google Scholar_, I have used other specialized academic search engines. I plan to contact someone at _Tropic Marin_ to see if he can help me.

JPC


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## sparkyweasel (25 Apr 2021)

It is surprising, especially when there is so much interest in the effects of fertiliser run-off into waterways.


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## X3NiTH (25 Apr 2021)

sparkyweasel said:


> The single mortality was a Chinook salmon tested at 200 mg/L KCl
> at low baseline water conductivity.



The way I see it is that “low baseline water conductivity” would suggest that K is the major ion in the water and as such the largest constituent for Total Hardness, you would be unlikely to see this in the wild unless from freshwater close to a source of Ultra Potassic rock but you’re still going to have lots of other major ions end up in that water.

Clives example is a balanced mix of ‘lots of everything’!

I’ve run 100ppm of K in GH 8 KH8 with Tetras without issue (on purpose). I suspect 0GH and 0KH with 100ppm K from only KCl long term wouldn’t be great but certainly not fatal in the short term, not many would be likely to do this anyway so it’s pretty much a non issue.

One fatality, I’d say that’s about a million miles from discovering the LD50% for Salmonids (was fry, juveniles or adult fish tested?).


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## sparkyweasel (25 Apr 2021)

X3NiTH said:


> One fatality, I’d say that’s about a million miles from discovering the LD50%


That's the conclusion they reached in the paper, with it being the only fatality, especially with "no obvious proximate cause of death".


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## MichaelJ (25 Apr 2021)

X3NiTH said:


> I’ve run 100ppm of K in GH 8 KH8 with Tetras without issue (on purpose).


@X3NiTH  That is good know! I should be quite a bit lower than that anyway.


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## X3NiTH (25 Apr 2021)

sparkyweasel said:


> That's the conclusion they reached in the paper, with it being the only fatality, especially with "no obvious proximate cause of death".



So the fish at the bottom of the pecking order then! “Quick guys they’ve stopped feeding us let’s do in Dave, nobody likes him anyway”


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