Seachem method of potassium dosing

[MiZubov]

No, not really.

In the end, it's up to you. A good starting point is nitrogen. How much nitrogen do you need? It depends primarily on CO2 & light. If you run high-tech, you'll probably need 10 mg/L NO3-, or maybe even more. In low-tech, see my chart above.
Nitrogen to phosphorus ratio is known, it should be around 16 : 1 [on molar basis]. Similarly, potassium to nitrogen is also a given: 1 : 4 [molar]. There may be more potassium, but not less.
As for K, Mg and Ca, there should be several times more Ca & Mg than K. Mg to Ca ratio is less important than people often believe. Only in hard waters, sometimes there's too much calcium and too little magnesium. If that is the case, you should add magnesium. A ratio 1 : 2 [again, molar] for Mg : Ca is ideal, 1 : 5 still acceptable for most plants.

But what about: "Calcium is an antagonist of many heavy metals, as well as phosphorus." So, there is a precipitation of phosphate in water with high calcium and it needs to be added more to maintain the correct N: P ratio?
I understand and take into account the ratio of Nitrogen and Potassium, but what are the ratios of elements with Calcium? So far, it turns out that there is nothing terrible in the fact that there is a lot of it, but in practice I see that plants do not feel well in water with a lot of Calcium…
On the other hand, I have a lot of carbonates, perhaps they are the reason for the poor growth of plants..

 

[_Maq_]

there is a precipitation of phosphate in water

Correct. Phosphates are prone to loss in precipitates. The main enemy is not calcium, though, but iron.
You can see that even in my soft water, I dose a bit more (15 %) phosphorus relative to nitrogen.

I see that plants do not feel well in water with a lot of Calcium

Some plants simply hate hard water, that's a hard fact. Yet there are still many which tolerate it, possibly some even prefer.

I have a lot of carbonates, perhaps they are the reason for the poor growth of plants

Correct. If you're using RO water and your rocks dissolve that quickly then you'll probably have to get rid of those rocks.
There's one more danger in that: It scavenges CO2. The reaction goes like this: CaCO3 (s) + CO2 + H2O -> Ca(HCO3)2.
Still, many aquarists use calcite rocks for decoration and the dissolution problems are manageable. What about your substrate? Is it rich in calcite?

 

[MiZubov]

Correct. Phosphates are prone to loss in precipitates. The main enemy is not calcium, though, but iron.
You can see that even in my soft water, I dose a bit more (15 %) phosphorus relative to nitrogen.

Some plants simply hate hard water, that's a hard fact. Yet there are still many which tolerate it, possibly some even prefer.

Correct. If you're using RO water and your rocks dissolve that quickly then you'll probably have to get rid of those rocks.
There's one more danger in that: It scavenges CO2. The reaction goes like this: CaCO3 (s) + CO2 + H2O -> Ca(HCO3)2.
Still, many aquarists use calcite rocks for decoration and the dissolution problems are manageable. What about your substrate? Is it rich in calcite?

What about iron?
How much NO3: PO4 do you keep?
How does the phosphate precipitation reaction occur? Let's say there are 0.1 phosphates in water, after adding calcium, it decreases and becomes inaccessible to plants? Or does it happen in some other way?

 

[dw1305]

Hi all,

Erm, yes but your starting point is rain water, so you have a big advantage, ie soft water

Point taken, it definitely makes keeping ions in solution easier.

I don't use rain water <"If it's yellow, let it mellow and RO is the devil"> specifically because of its softness, I use it because I've always used it, from long ago, back before <"I was a planted tank keeper">.

As Vin points out, the top right corner is blank.

I think I know the reason, from my experience of waste water work, you would grow a lot of green filamentous algae.

But what about: "Calcium is an antagonist of many heavy metals, as well as phosphorus." So, there is a precipitation of phosphate in water with high calcium and it needs to be added more to maintain the correct N: P ratio?

If you get a lot of calcium (Ca) ions in solution they will interfere with the uptake of less abundant cations, it is just a numbers game. <"Nutrient antogonism"> .

Phosphates are prone to loss in precipitates. The main enemy is not calcium, though, but iron.

Yes, ferric iron (Fe III) is the preferred precipitant for phosphate (PO4---) <"Iron phosphate">, but most phosphate compounds are insoluble. If you ignore sodium (Na) salts it is only really potassium and dipotassium phosphate (KH2PO4 & K2HPO4) that are soluble <"Potassium Carbonate (K2CO3) vs pH ?">.

cheers Darrel

 

[MiZubov]

it is just a numbers game.

If you ignore sodium (Na) salts it is only really potassium and dipotassium phosphate (KH2PO4 & K2HPO4) that are soluble

Can you explain these proposals a little more? I didn't understand…

 

[dw1305]

Hi all,

Can you explain these proposals a little more? I didn't understand…

It is only the phosphates of the alkali metals (sodium (Na), potassium (K) etc) that are soluble, so form 3Na+ and PO4--- ions.

This is fine if you only have Na+ ions in solution, but as soon as you have calcium (Ca++) ions etc. in solution? They form insoluble calcium phosphate (Ca3 (PO4)2) etc. precipitate out of solution and stop being plant available.

Cheers Darrel

 

[MiZubov]

Hi all,

It is only the phosphates of the alkali metals (sodium (Na), potassium (K) etc) that are soluble, so form 3Na+ and PO4--- ions.

This is fine if you only have Na+ ions in solution, but as soon as you have calcium (Ca++) ions etc. in solution? They form insoluble calcium phosphate (Ca3 (PO4)2) etc. precipitate out of solution and stop being plant available.

Cheers Darrel

Maybe you know..Why is there a lot of calcium in a marine aquarium, but the problem of phosphates is still difficult to solve there? There is always a lot of it and every time it is a problem

 

[dw1305]

Hi all,

Maybe you know..Why is there a lot of calcium in a marine aquarium, but the problem of phosphates is still difficult to solve there? There is always a lot of it and every time it is a problem

There are only trace amounts, but it is meant to effect the formation of the calcium carbonate (CaCO3) skeletons of hard corals etc.

You will need someone who has kept marines to tell you more.

Cheers Darrel