# K vs. N consumption by plants



## Bryeman (Aug 24, 2009)

Does anyone have a rough idea of how much K is consumed versus N in an aquarium? I'm not measuring the K in my tank, and don't plan on it, but would like to make my EI dosing to make sense (if K is typically used 10% more than N, I want to be adding 10% more K versus N type of thing).


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## Newt (Apr 1, 2004)

I find that K is used very slowly and very little is used unless lighting is very intense and then it picks up. PO4 seems to used very quickly followed by N. 
In EI dosing (I thought) K is not added as an individual nutrient but is found to be adequate from the K that is in KNO3 and KH2PO4.
I used to measure K regularily with a LaMotte kit but found it to be always present in more than adequate amounts so I only spot check infrequently now.

http://www.finostrom.com.gr/images/aqua/fertilizers/map.htm


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## Bryeman (Aug 24, 2009)

Thanks Newt. I currently add K2SO4. I've read some claim you don't need to add it, but some claim you do. I was just curious as to what the deal with K was. Something isn't quite right with my setup yet and I'm tryong to explore all possibilities. Plus I'm impatient and you know how well that works with this hobby!


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## bgzbgz (Jul 6, 2007)

Ideally the K needs to be in "balance" more or less with Ca and Mg in your water. In other words for hard water you'd want more K than for soft water.


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## MrSanders (Mar 5, 2006)

bgzbgz said:


> Ideally the K needs to be in "balance" more or less with Ca and Mg in your water. In other words for hard water you'd want more K than for soft water.


Could you tell me more about your experience with this? i have fairly soft water GH=4 KH=2, and seem to get a lot of weird issues with plant growth, health just not being where it should be. What sort of balance should be maintained between Ca, Mg and K? i know from a city water report that my water is just under 30ppm Ca and as well as just under 5ppm Mg.


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## bgzbgz (Jul 6, 2007)

Hi MrSanders your the guy from the pfertz thread huh lol. Ok a decent ratio would be:
4:4:1 
K:Ca:Mg
This would be in ppms.

If you want to take it even further you could do this:
NO3:K:Ca:Mg
4:4:4:1


But keep in mind that these are just ideal water parameters, and the uptake rates will not be the same for all of the nutrients above.
See nice and easy to read/understand right?


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## wet (Nov 24, 2008)

Do you have a reference to cite for those ratios, bgzbgz? Agree in the general sense of no limits but simply curious. In both my hard (tap) and soft (reconstituted RO) water tanks I've not found any issue with K, and think the Ca/Mg relationship overmanagement of nutrients.

Bryeman,
Remember that the max limit under EI with 50% water changes is twice the input. When following this method you should not worry about ratios so much with your goal instead being no limiting nutrients. As Newt, I am of the camp whose regular uptake is so high that the NO3 input from KNO3 ensures that K is not a problem, but I drop in nuggests of KCl (as "Sodium-free water softener") on the regular (every water change or less) for peace of mind. EI is more practical with high uptake tanks, where you'll find most proponents simply dose to excess and trim regularly/pwc for nutrient export. But you probably know that already...


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## Diana K (Dec 20, 2007)

I use the plants to test for K. When I drop the dosage, holes show up in the leaves. When I increase the dosing the new leaves come out looking good, and do not develop holes.

I test for NO3, and most of my tanks have lots of fish, so I do not dose enough KNO3 to keep up with the need for K. The fish food provides enough N to keep most of the tanks testing at about 5-10 ppm NO3.

It is not the ratio in the fertilizer you need to look at, but the ratio of all the things that go into the tank.

Water: test it separately, with no aquarium additives. Read the report from your water company. This is especially helpful if you can get several years' reports and see how consistent the water is. A water source with lots of minerals, or a well in an agricultural area might almost test like a fertilizer. (A friend's well in an agricultural area tests 10 ppm Nitrate, for example!)

Fish Food: Lots of fish or few fish are not actually the source of fertilizer. It is the fish food. If you had no fish, but still added a pinch of fish food twice a day, that is fertilizer. Whether it is digested by fish or bacteria is not an issue. Fish food is a fertilizer. Fish are simply a system of breaking down fish food into pieces the bacteria can handle quicker to turn it into plant food.

Other additives: I make harder water for my Lake Tanganyikan tanks with either Seachem Equilibrium or Barr's GH Booster. Either of these add a lot of K, as well as Ca, Mg and some other things. Some people add pH adjusting products that might be high in phosphates or other fertilizers.

Nutrients from the substrate: Complex issue here:
If your substrate is fairly active, high CEC, then it might be holding onto some of the fertilizers you have been dosing. Then, even if you did a water change the fertilizers are still there for the plants' roots to get. 
If you are working with an older (used) substrate, or one of the plant specific substrates there might already be fertilizer in there. How do you know how much, what, and when it runs out?
If the substrate or filter has material that dissolves to become plant nutrients this is another source. Limestone and coral sand, for example as sources of Ca, Mg and carbon (from carbonates). Larger rocks in the tank dissolve slowly, so they may or may not count as fertilizer. They do contribute something, but such a low level it may not make much of a difference in the tank.

So: N:K ratio in fertilizer is not in itself important. Look at _all_ the things you add to the tank, perhaps try to balance all the additives by altering the fertilizer amounts and dosing and monitor the plants to see if things are going well.


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## Philosophos (Mar 1, 2009)

N:K is something simple if growth is all you're after; I have yet to see deficiencies at 20ppm K and 20ppm NO3. Once it's all non-limiting and luxury uptake has been satiated somewhat, you've got nutrients nailed down for healthy growth. K is a bit of a confusing issue, but it's not very toxic to fauna so dosing 20ppm along side NO3 isn't likely to hurt. There's a bit of bantering somewhere about K+ and Ca uptake, but nothing I've seen nailed down.

At the same time, if you're headed for growth forms in various plants then who knows what you'll run into. There's so little published in the hobby about dimorphism. Growing weeds for aesthetic purposes is inconceivable to the government (under) funded scientists who have jobs working with these plants in nature; you'll find hints in their papers but rarely a central focus. Your messing around with plants and some casual observations might be worth chasing as something to add to the hobby. For an example from my own trays, I've got one little bit of very pink/red P. Helferi growing emersed out of a substrate that should have tons of N and P. I can't explain it, I won't give in to conjecture, but I'm going to keep it in mind so that I can try to reproduce it later.


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