# Role of potassium in and out of water



## kschyff (23 Aug 2022)

Hi,
I have a question about potassium in relation to its use as a fertilizer. When I use Aquasoil (which they say has no K) in a dry start all the plants grow like crazy without any issues. I spray with RO water and all is well as far as I can see. In other words, there is growth without the addition of K. However, when I flood the aquarium all of a sudden I have to dose K. I am not a biologist, but maybe someone can explain this to me. The AS I use specifically states that there is virtually no K in it.

I am reaching here when I say the following: In another aquarium where I use a peat-based substrate covered with inert gravel, I dose EI (full) but leave out the micros as the manufacturers state that I should avoid this for the first 3 months. To add minerals I use MgSO4 and CaCl. As per the Fert calculator. In this aquarium I notice yellowing in my crypts with dark veins, stunted and curled leaf tips etc. So I try a some research and found an academic article that states that for terrestrials plants too much K can cause problems for magnesium uptake.

Am I way off track? If so, please correct my thinking here.


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## dw1305 (24 Aug 2022)

Hi all,


kschyff said:


> When I use Aquasoil (which they say has no K) in a dry start all the plants grow like crazy without any issues





kschyff said:


> I am not a biologist, but maybe someone can explain this to me


I think the aquasoil doesn't have any <"*added* potassium"> (K), rather than not having any potassium at all. Potassium is one of the mineral elements that plants need most of.


kschyff said:


> ....... In another aquarium where I use a peat-based substrate covered with inert gravel, I dose EI (full) but leave out the micros as the manufacturers state that I should avoid this for the first 3 months. To add minerals I use MgSO4 and CaCl. As per the Fert calculator. In this aquarium I notice yellowing in my crypts with dark veins, stunted and curled leaf tips etc. So I try a some research and found an academic article that states that for terrestrials plants too much K can cause problems for magnesium uptake.


One for @_Maq_, but I'm going to guess it is more likely to be a microelement deficiency.

cheers Darrel


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## plantnoobdude (24 Aug 2022)

dw1305 said:


> Hi all,
> 
> 
> I think the aquasoil doesn't have any <"*added* potassium"> (K), rather than not having any potassium at all. Potassium is one of the mineral elements that plants need most of.
> ...


Perhaps it is a deficiency, but photos are needed.


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## kschyff (24 Aug 2022)

@dw1305 thank you.


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## kschyff (24 Aug 2022)

@plantnoobdude I have added the photos here. I have csm+b, but because they say the substrate has all the micro elements it needs I have not added any. I must be honest it never really grew well at all. Have a look at the pictures I uploaded. This was 4 days ago and the repens has almost completely disappeared now. For some reason the AR seems ok.


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## _Maq_ (24 Aug 2022)

Unfortunately, symptoms are often difficult to read - for me, at least - without accompanying data. Par example, look at the following picture (_Ludwigia glandulosa_):



These Ludwigias clearly show some nutrient deficiency, but which one? One could guess iron, manganese, magnesium, maybe others... Yet I knew exactly the composition of the water I poured in (and the substrate was plain silica sand), and _only thanks to that_ I could find the right answer. The following pic shows the same plants seventeen days later:



You can see that the older leaves kept their interveinal chlorosis, but the newer ones are fairly green. That proved that my diagnosis of the *first* deficiency (and adjustment of nutrients according to it) was correct. But the newer leaves are a bit twisted. In this *second* case the diagnosis was much easier: relative calcium deficiency. The reason was potassium to calcium ratio 1 : 1, too much potassium relative to calcium (and magnesium). Yes, @dw1305 remembers correctly that I'm a proponent of high Ca : K ratio, 10 : 1 at best.
Yet even in this easier case I wouldn't be very sure because slightly twisted leaves may also signal boron, chlorine, or copper deficiency, or toxicity of some nutrients. Only because I _knew_ there was too much potassium there, diagnosis was easy.
----
What I want to say? Yes, I can see in your pics some hints at possible magnesium, calcium, nitrogen, boron, sulfur, iron, manganese, or zinc deficiencies. In most cases I'm probably wrong. I'd like to know following (ranked from most important to least important: pH, alkalinity, electric conductivity, that dark-gray gravel - what is it?, content of major cations (Ca, Mg, Na, K), dosing of nitrogen and phosphorus. With such data, we can "see" more and may attempt to suggest a successful remedy.
----
Lastly, *just for fun! *Can anyone tell what nutrient had been missing in the first case (interveinal chlorosis)?


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## plantnoobdude (24 Aug 2022)

_Maq_ said:


> Lastly, *just for fun! *Can anyone tell what nutrient had been missing in the first case (interveinal chlorosis)?


Zinc? 
Beautiful pics btw.


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## kschyff (24 Aug 2022)

Thank you for the excellent explanation. To be honest I may have difficulty providing some of those. Let me start with what I do know for now then tick off the others when I get reliable equipmemt to measure the pH for example.

1) Nitrogen and phosphorus is as per the fert calculator for full EI. The calculator is set for a 30 litre wc out of the 50 total litres. Remineralize as per calc using CaCl and MgSO4. These are dry dosed about 5 minutes apart at wc.

2) I am not sure about the gravel but I was told its inert. I suppose this is a mystery but if I know what to test for I could take the water to a lab. Something exotic might appear?

3) Is the conductivity simply the TDS reading?

4) The alkalinity is sitting at 0 to 1 with gH at 5. Its RO water.

5) The pH I will have to measure with a reliable pen. Sorry about that. I know its no1 on your list. The injection rate is really high and its on 24/7 as I thought I would go for a very consistent CO2 level. None of the fish are suffering.

6) I am not dosing CSM+B at all. The substrate Aquaforest AF says it contains enough for 3 months. I am almost into month 3.

7) The cations I am not sure about as I have no idea how to measure it.



Sent from my SM-A715F using Tapatalk


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## jaypeecee (24 Aug 2022)

_Maq_ said:


> Unfortunately, symptoms are often difficult to read - for me, at least - without accompanying data.


Hi @_Maq_

I am greatly reassured by your statement immediately above. Now I can feel more comfortable knowing that I'm not alone when relying solely on vision to determine the nutrient(s) in short supply.

JPC


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## KirstyF (24 Aug 2022)

_Maq_ said:


> Lastly, *just for fun! *Can anyone tell what nutrient had been missing in the first case (interveinal chlorosis)?



Well I’ll stick my neck out for a giggle. The issue and the solution are both showing on new leaves so I’d say an immobile nutrient. Fe would be the go to for interveinal chlorosis for me but that would be way too easy so I’m going to go for Mn! 😊


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## KirstyF (24 Aug 2022)

Edit: Double post


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## dw1305 (25 Aug 2022)

Hi all, 


kschyff said:


> Is the conductivity simply the TDS reading?


Yes, but the <"other way around">.  For most conductivity meters 64 ppm TDS is actually 100 microS.


kschyff said:


> Remineralize as per calc using CaCl and MgSO4.


I'm going to say that you don't have a deficiency of either magnesium (Mg) or calcium (Ca). You need to take the <"water of crystallization"> into account when you do this calculation. 


jaypeecee said:


> I am greatly reassured by your statement immediately above. Now I can feel more comfortable knowing that I'm not alone when relying solely on vision to determine the nutrient(s) in short supply.


Problematic for <"the mobile nutrients">.


KirstyF said:


> The issue and the solution are both showing on new leaves so I’d say an immobile nutrient. Fe would be the go to for interveinal chlorosis for me but that would be way too easy so I’m going to go for Mn!


Less problematic for the <"non-mobile ones">.

cheers Darrel


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## Hufsa (25 Aug 2022)

I might be missing the point here, but can OP not dose N, P, and K, plus traces? Wont need to worry about what might or might not be in soil. Especially since the plants are struggling without it?


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## JoshP12 (25 Aug 2022)

kschyff said:


> Hi,
> I have a question about potassium in relation to its use as a fertilizer. When I use Aquasoil (which they say has no K) in a dry start all the plants grow like crazy without any issues. I spray with RO water and all is well as far as I can see. In other words, there is growth without the addition of K. However, when I flood the aquarium all of a sudden I have to dose K. I am not a biologist, but maybe someone can explain this to me. The AS I use specifically states that there is virtually no K in it.
> 
> I am reaching here when I say the following: In another aquarium where I use a peat-based substrate covered with inert gravel, I dose EI (full) but leave out the micros as the manufacturers state that I should avoid this for the first 3 months. To add minerals I use MgSO4 and CaCl. As per the Fert calculator. In this aquarium I notice yellowing in my crypts with dark veins, stunted and curled leaf tips etc. So I try a some research and found an academic article that states that for terrestrials plants too much K can cause problems for magnesium uptake.


In dry start, all nutrients come from soil and the composition is made of nature and is “fantastic for balance around roots” … no one is denying nutrient interactions in soil in agriculture and their effect on general yield etc … so let’s assume that these soils for aquasoils are “pretty close to perfectly balanced”. 

When we flood, we should consider the acquisition of those nutrients at the leaf etc that is submerged— so the plants gets its nutrients from two places now and nature didn’t make your water and pick your species etc …. So it may be a good idea to dose K not for leidbig but for the proverbial “balance”. 

The alleged ratios never get used up to 0 after 1 week, but people swear by 30/18/10 ca/k/Mg and it works …. But not for leidbigs law of the minimum. 

Ei originally didn’t call for GH booster, then suddenly it was called for because “we run out minerals maybe” … “let’s just make sure it’s there” …. go ahead and try to consume 10ppm of Ca in a week with laser and massive co2 injection. Perhaps it was: let’s slow this force feeding of N and P down because it’s driving the system so flipping hard that our injection and flow can’t keep up unless we have no livestock or infrastructure in place to facilitate perfection. Or try to provide some structure to a range of extremely influential parameters. 

That’s my take on it.

Am I way off track? If so, please correct my thinking here.
On the contrary.


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## jaypeecee (25 Aug 2022)

JoshP12 said:


> ...people swear by 30/18/10 ca/k/Mg and it works


Hi @JoshP12 

Not so long ago, I asked about an optimum ratio of nutrients in our tanks. I'll see if I can track it down. But the outcome of the discussion was that there possibly wasn't an optimum ratio. In your post above, you said "people swear by 30/18/10 ca/k/Mg and it works". Referring to Diana Walstad's _Ecology of the Planted Aquarium,_ Table VII - 2, the 'sworn by nutrient ratio of 30/18/10' doesn't seem to tally with either the Critical Concentration or the 'Elements Found in My Plants' column of Ms Walstad's book.

Are you able to shed some light on this? It's quite likely that I'm just not understanding these figures and their corresponding ratios. Please enlighten me!

JPC

P.S. If I'm not making myself clear, I'll try again tomorrow, hide away or go to the back of the class!


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## JoshP12 (26 Aug 2022)

Hi @jaypeecee ! 

I don’t think there is an optimal ratio as it would be unique to the soil conditions, the particular adaptations of the plant, and the species, and the microbiology etc.

But I think those sacred values I quoted are like the word on the street … and lots and lots and lots of people just use them and have massive amounts of success. 

That is GH 5-7. 

I’ve tried them all and it just makes things “easier” — softer water, less ferts, less co2, … needs more keener observation to predict algae and you have less time to react. GH5-7 gives you time with that potassium gives you a bit more wiggle room and time to react - at least in my experience. 

Can’t say I have any qualifications to make me an authority or shed any particular light. I studied pure maths and chemistry and I’m in the education field … just happened to become obsessed about this hobby, read the papers, the books, etc and I’m not entirely sure if anyone shares my view on the system and system thinking - specifically about nutrient acquisition. 

Josh


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## Ria95 (26 Aug 2022)

kschyff said:


> When I use Aquasoil (which they say has no K) in a dry start all the plants grow like crazy without any issues. I spray with RO water and all is well as far as I can see. In other words, there is growth without the addition of K. However, when I flood the aquarium all of a sudden I have to dose K. I am not a biologist, but maybe someone can explain this to me. The AS I use specifically states that there is virtually no K in it.


One aspect is that plants can manage for a while (months?) with little additional K, just stunt their growth. Stunted growth can be hard to notice when you don't have a plant growing in good conditions so deficiencies go unnoticed for a long time. 

Worth mentioning  that most aquasoil analyses  show plenty of K in their composition. For example, Tom Barr mentioned 554 mg/kg and 390 mg/kg  for ADA Aquasoil Old and New. Other soils have similar figures, they would be pretty poor plant soils if they lacked a major macronutrient.  Maybe the manufacturers  meant to say that 'virtually no K' from the substrate will be present in the water column?  Sure, if we were to take 1kg of Aquasoil and somehow extract all the K in a 100L it would only be 5 mg/L. Not a lot, but that's not how soils work. Absent a standardized soil analysis for your soil, who knows.  



kschyff said:


> 1) Nitrogen and phosphorus is as per the fert calculator for full EI. The calculator is set for a 30 litre wc out of the 50 total litres. Remineralize as per calc using CaCl and MgSO4. These are dry dosed about 5 minutes apart at wc.
> 
> 6) I am not dosing CSM+B at all. The substrate Aquaforest AF says it contains enough for 3 months. I am almost into month 3.


Looking at the  Rotala macrandra in your photos I would say you need to dose  micros. Why not have some micronutrients in the water column as well? The soil may still provide some for the plants that have extensive root systems to reach a rich area,
In general, if your plants are showing growth issues,  it may be worth starting to dose whatever it is you are omitting.



JoshP12 said:


> The alleged ratios never get used up to 0 after 1 week, but people swear by 30/18/10 ca/k/Mg and it works …. But not for leidbigs law of the minimum.





JoshP12 said:


> But I think those sacred values I quoted are like the word on the street … and lots and lots and lots of people just use them and have massive amounts of success.
> 
> That is GH 5-7.



The fantastic power of ratios is that a ratio of Ca:K:Mg cannot only give a GH of 5-7.
 Having 30 mg/L Ca and 10 mg/L  Mg will give you 6.5. At the same ratio you get a GH of ~20 ( 91 mg/L Ca, 30 mg/L Mg  and 54 mg/L K). At the same 'sacred' magic ratio 30/18/10 Ca:K:Mg, you may get a GH of 1 (4.4 mg/L Ca, 1.5 mg/L Mg, 2.7 K).  I've never seen  proponents of ratios recommending  54 mg/L K, but rather point to such high values as the source of all troubles. If 'sacred' ratios are what keeps us from success,  it follows that plants should grow the exact same  in all the above situations and even beyond. Do they?


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## JoshP12 (26 Aug 2022)

Ria95 said:


> The fantastic power of ratios is that a ratio of Ca:K:Mg cannot only give a GH of 5-7.
> Having 30 mg/L Ca and 10 mg/L  Mg will give you 6.5. At the same ratio you get a GH of ~20 ( 91 mg/L Ca, 30 mg/L Mg  and 54 mg/L K). At the same 'sacred' magic ratio 30/18/10 Ca:K:Mg, you may get a GH of 1 (4.4 mg/L Ca, 1.5 mg/L Mg, 2.7 K).  I've never seen  proponents of ratios recommending  54 mg/L K, but rather point to such high values as the source of all troubles. If 'sacred' ratios are what keeps us from success,  it follows that plants should grow the exact same  in all the above situations and even beyond. Do they?


Nope. I’ve expressed the same sentiment in other threads.


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## jaypeecee (26 Aug 2022)

JoshP12 said:


> But I think those sacred values I quoted are like the word on the street … and lots and lots and lots of people just use them and have massive amounts of success.
> 
> That is GH 5-7.


Hi @JoshP12 

Many thanks for your reply.

It's all starting to make sense now. Phew!

JPC


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## _Maq_ (26 Aug 2022)

_Maq_ said:


> Lastly, *just for fun! *Can anyone tell what nutrient had been missing in the first case (interveinal chlorosis)?





plantnoobdude said:


> Zinc?





KirstyF said:


> Fe would be the go to for interveinal chlorosis for me but that would be way too easy so I’m going to go for Mn! 😊


Pretty rare case of *sulfur* deficiency.


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## _Maq_ (26 Aug 2022)

jaypeecee said:


> Not so long ago, I asked about an optimum ratio of nutrients in our tanks. I'll see if I can track it down. But the outcome of the discussion was that there possibly wasn't an optimum ratio.


The issue gets much more complicated when there's any clay in the substrate. A few basic facts about clay minerals:
(1) Clays possess a cation exchange capacity. Let's always keep in mind that a proton (H+) is also a cation, and can occupy an exchange site.
(2) There are many kinds of clay minerals originating from many deposits. Each and every of them comes with some amount of cations bound, and each has its own affinity for every cation.
(3) This affinity interacts with outer environment. Par example, such a clay may accept more protons in acidic water while releasing some other(s), again in respect to their abundance.
Now, plants - not even species, but often even individual plants - differ in their dependence on nutrients taken up from substrate or water column. Obviously, if there are substances with adsorption capacity (a broader term than CEC) within the substrate, the ratios among elements are different in the substrate and the water column.
I've been studying nutrient ratios for quite a while. To minimize the influence of substrate (and its compounds with adsorption abilities) I stick to clean (acid washed) silica sand. Still, I can't avoid some detritus accumulation in the sand. (I don't vacuum it not to disturb microbes living there.) Detritus too has significant adsorption ability.
In sum: If we all kept our tank fishless and with plain silica sand, then our results with nutrient ratios could be somehow compatible. Naturally, only if we use RO+DI water mineralized with *all* nutrients following some coherent pattern. In all other instances the experience of any aquarist is largely individual, not directly applicable in different conditions.


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## KirstyF (26 Aug 2022)

_Maq_ said:


> Pretty rare case of *sulfur* deficiency.



I was never gonna guess that! 😂


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## John q (26 Aug 2022)

_Maq_ said:


> The issue gets much more complicated





KirstyF said:


> I was never gonna guess that! 😂


🤪


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## jaypeecee (30 Aug 2022)

Hi @_Maq_ 

I must apologize for not replying to your post #21 above. For some reason, it escaped my attention.

At present, I only have one tank in operation and the 'substrate' is simply a 2 cm layer of silica sand.

JPC


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