# K2S04 vs KH2PO4



## heidisue (May 3, 2006)

When did the Barr method of ferts switch from emphasizing K2S04 to KH2PO4? Why? I missed that memo and can't find from searching.


----------



## banderbe (Nov 17, 2005)

heidisue said:


> When did the Barr method of ferts switch from emphasizing K2S04 to KH2PO4? Why? I missed that memo and can't find from searching.


Lots of the 'old school' guys don't dose K2SO4 at all. They believe you get enough from KNO3 and KH2PO4.

I learned this a few months ago, stopped dosing K2SO4, and my tank looks great and the plants are happy. I can't say it improved anything but it sure didn't hurt and now I don't have to buy K2SO4!


----------



## hoppycalif (Apr 7, 2005)

K2SO4 is a good source of potassium, but KH2PO4 isn't, both because it contains a lot less and because we dose such small quantities of it. But, KNO3 is a good source and we dose a lot of it. I think I have read that potassium is not a critical fertilizer - it needs to be available, but not in some carefully measured amount. So, I have never dosed K2SO4. (Hmmm, could that be part of my algae problem???)


----------



## John N. (Dec 11, 2005)

Potassium (K) plays a minor role in a plant metabolism. Often times plants will absorb excess K and keep it for storage. K is an important element that regulates photosythesis, creates ionic balance, and most important activates enzyme production that stimulates plant growth and uptake rates.

Provided that one is dosing both KNO3 and KH2PO4, then enough potassium will be dosed. Plants don't require high levels of Potassium so the extra boost from K2SO4 isn't necessary. However, when one is having some potassium deficiency in plants, it does come in handy to dosing K2SO4 separately from everything else. 

-John N.


----------



## perpacity (May 30, 2006)

If the puprose of using the above compounds is to introduce potassium, then what are the advantages of using said compounds instead of KHCO3 or K2CO3?


----------



## czado (May 26, 2005)

Neither K2SO4 nor KH2PO4 will raise KH, but the carbonate from KHCO3 and K2CO3 will. As said, the purpose of KH2PO4 is more for phosphate than potassium, though its potassium content is a nice bonus.

I like and find/think my plants do better with excess K, and I dose with KCl, for what its worth. Many prefer K2SO4 since it avoids the salts and possible detriment of Cl-.


----------



## heidisue (May 3, 2006)

John N. said:


> Provided that one is dosing both KNO3 and KH2PO4, then enough potassium will be dosed.


So if I'm just dosing KN03 and K2S04, would fleets complete my macros? Is it only phosphate that I'm missing?

Also dosing flourish, btw.


----------



## dennis (Mar 1, 2004)

Yep, you got it.

Here is a basic breakdown of what the different ferts add:
per 1gram in 10 gallons:
KNO3- 16ppm NO3, 10ppm K
KH2PO4- 18.5ppm PO4, 17.5ppm K
K2SO4- N/Appm SO4, 11.9ppm K
Fleet(1ml)-17.7ppm PO4, should add some K also

Obviously those are not amounts you may use in a tank, just an easy frame of reference. As you can see, KH2PO4 adds PO4 and K in roughly 2.5:1 ratio. So, if you add 1ppm PO4 to your tank, you only add .4ppm K. KNO3 adds NO3 and K in a 1.6:1 ratio so every 10ppm NO3 added to your tank also gives 6.25ppm K.

A frequent high light dosing schedule is 10ppm NO3 and 1ppm PO4 four times a week. This adds 6.65ppm K at every dose and from my reading this should be plenty of K. Adding more would not hurt anything but is _probably _not necessary.

So, we add KNO3 for NO3 but it generally gives us enough K also. KH2PO4 also gives a fair amount of K in relation to PO4 by weight; however, we use so little PO4 in our tanks that the K added is negligable. Therefore, the main benefit from KH2PO4 is PO4.


----------



## heidisue (May 3, 2006)

Wow - thanks for the breakdown, Dennis! Very helpful to know what we're emphasizing when we dose each compound.


----------



## BryceM (Nov 6, 2005)

Dennis,

I assume you are taking your numbers from the fertilator. Just FYI, there is still a bug in the entry for Fleets. Each ml of fleets contains between 131mg and 150mg of PO4, depending on which numbers you use. In 10 gallons, one ml provides about 3.5 ppm of PO4. It also adds a small quantity of sodium, but no potassium (K).


----------

