The potasium in potasium nitrate - The Planted Tank Forum
 
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post #1 of 12 (permalink) Old 09-15-2014, 02:40 PM Thread Starter
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The potasium in potasium nitrate

I got some Potassium Nitrate, aka Saltpeter, understanding that its a decent "N" source.

This may be a really stupid question, but does it not contain potassium (K) as well? Or is it in a format which plants can/wont use, different from the potassium in Potassium Sulfate?
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post #2 of 12 (permalink) Old 09-15-2014, 03:11 PM
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Potassium Nitrate is what is most commonly used for K. Often labeled KNO3.
The Potassium Sulfate, labeled K2SO4 is substituted when the fish stocking level is high causing the NO3 to be there already and you don't want to add more of it by using KNO3. Since I just started this a year or so back some detail of what I said may be off a tad but mostly in the correct direction.
It raises your nitrates a bit so if the bio-load is already high from lots of fish then the substitute. But it normally is what goes with KH2PO4 as the Macros.

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post #3 of 12 (permalink) Old 09-15-2014, 03:34 PM Thread Starter
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So in a low-load setup, the Potassium Nitrate may be all you need to dose for Macro?
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post #4 of 12 (permalink) Old 09-15-2014, 04:29 PM
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No it's either KNO3 and KH2PO4 or K2SO4 and KH2PO4.
Fert "Plans" or "Systems" are not a perfect fit for every tank and the type and amount of plants it contains. But they are a starting point to work from.
In the fert sction on the first thread there is "yet another calculator" and you shouls eventually get to know it if you want to have a sucessful planted tank.
I'm still trying to figure it out myself but also on that thread there is a guide for dosing.
There are several sources for dry ferts but I think it's Greenleaf will help you decide what is best for your tank.
Also putting a list of what light, possible CO2 etc of your tank on the fert section can get someone on here who will help/w that.

The shortest distance between any two points is a straight line...in the opposite direction...
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post #5 of 12 (permalink) Old 09-15-2014, 05:17 PM Thread Starter
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I've read all about EI but was just curious why NO3 is regarded only as an N source and not also K.

According to wiki, KNO3 has an NPK fertilizer value of "13-0-44".... which seems like a lot of K per dose. But maybe that's the right amount in relation to N?

For example, a typical EI for 10-20G calls for :
1/8 tsp KNO3 (N)
1/32 tsp KH2PO3 (P)
And no K

So I'm guessing the K must be assumed to be part of the KNO3 (though its always referred to as N only).
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post #6 of 12 (permalink) Old 09-15-2014, 05:48 PM
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That depends on plant uptake. Hygrophila's uptake K at very high rates so the K in KNO3 may not be sufficient.

KNO3 is both regarded as an N and K source.
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post #7 of 12 (permalink) Old 09-15-2014, 05:58 PM
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Potassium Nitrate, KNO3 (saltpeter) is 38.6% Potassium (K) and 61.4% Nitrate (NO3), water is “powerful” enough to separate the Potassium from the Nitrate, in this form they carry a formal charge so we write these forms as K+ and NO3-, the water is not “powerful” enough to separate Nitrate into Nitrogen and 3-Oxygen atoms.

KNO3 is a good source of Potassium and Nitrate for our tanks. When sold as fertilizer it has an NPK listing as 13-0-44, due to purity the KNO3 sold by most planted tank fertilizer may be 13-0-46. I am aware of one that lists the NPK as 13.2-0-46.5, I tested and found they were correct.

Potassium sulfate K2SO4 is 44.8% Potassium and Monopotassium phosphate, KH₂PO₄ (MKP), is 28.7% K+ and 69.7% Phosphate (PO43-).

Just find a method, I like the Estimative Index (EI), stick to the routine, observe the plants and everything will be fine.

Joe

Last edited by JoeRoun; 09-16-2014 at 06:14 AM. Reason: 2
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post #8 of 12 (permalink) Old 09-15-2014, 06:03 PM
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Also don't forget the dose listed is one of three per week.
Regular EI consist of three doses per week each of the Macos(which that is) and of
the Micros. Wisteria is also a plant which uses larger amounts of Potassium than normal.

The shortest distance between any two points is a straight line...in the opposite direction...
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post #9 of 12 (permalink) Old 09-15-2014, 10:04 PM
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Quote:
Originally Posted by Ziggy View Post
I've read all about EI but was just curious why NO3 is regarded only as an N source and not also K.



So I'm guessing the K must be assumed to be part of the KNO3 (though its always referred to as N only).
KNO3 has always been said, correctly, to be the source for both potassium and nitrogen. It is only when you decide to dose less, or no nitrogen, that you need to dose potassium separately, usually as K2SO4

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post #10 of 12 (permalink) Old 09-16-2014, 02:43 AM
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Many of my tanks have a moderate bio load, so I am dosing both KNO3 and K2SO4.
Less KNO3 than EI suggests because I have found the right dose that maintains the NO3 at about 10 ppm.
I substitute K2SO4 at the same rate because the tanks do need more K than I am dosing with the KNO3.

The K in KH2PO4 pretty much does not count, because it is dosed in such small amounts.

The EI method does treat the KNO3 as a source of both K and NO3.
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post #11 of 12 (permalink) Old 09-16-2014, 06:17 AM
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Smile Love Them Nitrates

KH2PO4 is about 28.7% K+ and 69.7% PO43-, leaving only 1.6% H+.

Nitrates that are from salts are not a particular problem, no reason not to dose plenty of excess.

Many have become concerned with excess sulfates and are avoiding K2SO4. I think this tends to be people monitoring water quality measuring conductivity.

Joe
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post #12 of 12 (permalink) Old 09-17-2014, 01:03 AM
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I've always been told you can't OD on potassium too. I always dose a little of K2So4 though and less KN03 then EI recommends.
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