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So far I have been fertilising my tank using KNO3 and Seachem's Potassium and Phosphate additives because I never found KH2PO4 in Britain. Now, however, I found a source of potassium phosphate but have also found information about K2HPO4 and I'm not sure which of the two this potassium nitrate is.

Now, is there much of a difference between the two? Can I use either to the same effect? Will the plants be able to use both in the same way?

Never even had one hour of chemistry in my life and everything I know (not a lot) comes from fishkeeping so any help is very appreciated.

Potassium Nitrate is KNO3
Potassium Hydrogen Phosphate is K2HPO4

you are right about these

as you can see that KNO3 contains a K cation and NO3 anion
therefore it supplies to the water potassium and nitrate ions

and K2PO4 contains 2 K cations and H cation and PO4 anion
therefore it supplies to the water potassium, hydrogen and phosphate

hope that clears up a little bit for you

Thanks for the reply.

I know about KNO3, my question is about whether I can use K2HPO4 to dose potassium and phosphate instead of KH2PO4. I understand that the first has two cations of K and one H and the second has one cation of K and two of H, but I don't understand if there's any difference between them regarding plants' needs?

2 K cations and H cation and PO4 anion

actualy (no hard feelings JQW) the cation is K2H+ and anion is PO4- cause there can only be one cation and one anion but close enough

well i think that the potasium nitrate would be a better option cause according to JBL phosphate is much less common in nature than nitrate. and so each ppm of PO4 is more critical as far as over doing it goes and triggering an algea burst.

declan

Thanks again for your answers.

Again, nitrate is not an issue, so we can forget about KNO3. The main question is whether K2HPO4 would be a good potassium and phosphate fertiliser, or, in other words, can I buy it instead of KH2PO4?

cation is K2H+ and anion is PO4-

oh well, i'll take it as you are right
but i thought there is no such thing as K2H or KH2 or KH because they dissociates fully in water into K ions and H ions
that was in unit 3 chemistry, now i'm in unit four so i'm safe
ops, my unit 3 exam, now i'm worried

K2HPO4 and KH2PO4 ummmm *rubs my chin*
again, correct me if i am wrong
from the equation K2HPO4 contains 2 lots of potassium where KH2PO4 contains only 1 lot of potassium
however, the first one has higher molecular weight hence same amount of sample would yield less potassium
hence i conclude that the latter one would give you more potassium than the first one given the weight of sample is the same

Guys,

I am getting dizzy just reading this thread :%):%):%)

For normal people with a lower degree in chemistry (like me), what products are you debating?
Or are you actually mixing your own soup?

Thanks,

Ingo

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Proud Member of the New Jersey Aquatic Gardeners Club

Ingo,

The issue doesn't regard a brand name product, that would make things much simpler.

With CO2 enriched tanks you often need to dose macro nutrients which the plants use very quickly -- those are nitrate, pottasium and phosphates. You can buy bottled fertilisers which is the easy way or you can buy chemical substances such as KNO3 (potassium nitrate) and KH2PO4 (potassium phosphate). This is the cheaper option, much cheaper.

I couldn't find KH2PO4 here in Britain so I wanted to know if I can use K2HPO4 instead. I understand that this has more potassium and less hydrogen, which really tells me nothing, my question (which I thought was a simple one...) was whether I can use that one instead of the KH2PO4 which is what everybody else uses.

This may be a silly question, someone may come up and say "you stupid, it's potassium and phosphate, doesn't matter how much hydrogen there is in there", which is what I'm hoping to hear. However, as I have no chemistry knowledge I thought there might be an issue that restricts me from using it... However, I seem to have gotten myself messed up with things like molecular weight...

Anyway, anyone can anyone come up with a yes/no answer for the question of whether K2HPO4 will supply my plants with potassium and phosphate? The dosage will be modified according to the plants' needs rather than me having to weigh molecules...

Last edited by untitled at 08-Jul-2005 09:38

I know that [link=Greg Watson]http://www.gregwatson.com/products.asp?cat=8" style="COLOR: #FFFF00[/link] has some monopotassium phosphate. He is reputable amongst some of the plant gurus on the web. I haven't personally purchased from him, but I've seen the link from many different people on the web. You can see if he'll ship some out to you. He actually has is own forum on [link=APC's site]http://www.aquaticplantcentral.com" style="COLOR: #FFFF00[/link]. You can register for free and post a question to him there if you like.

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Critical Fertilator: The Micromanager of Macronutrients

" my question is about whether I can use K2HPO4 to dose potassium and phosphate instead of KH2PO4."

Yes.

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http://justanothertank.com

btw, if you're trying to reach target K of 20ppm, either potassium phosphate* isn't going to get you there unless you overdose PO4. Consider K2SO4 or KCl, too. Its very possible to get away with lower K dosing from just KNO3 and KH2PO4 or K2HPO4, depending on how much you dose (use Chuck Gadd's calculator if you don't like the math of mass percentage). The important thing is to keep K available in decent quantity.

*=edit

Last edited by czcz at 08-Jul-2005 16:24

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http://justanothertank.com

Thanks for all your answers. This has explained something about chemistry and also gave an answer to my question.

Cheers.