Is precipitation really bad ?

[eminor]

Hello, i did a macro solution using :

• 808 ml of Ro Water
• 28g K2SO4
• 4g PO4
• 20g KNO3
• 32g KCL
• 6g Urea

I first added the ro water, then added salts in the order above, the hardest to dissolve to the easiest, there is a small amount of white powder on the bottom if i let it still ( 2 mm) , does that mean that the ferts are bad/ non effective ? thx

 

[Wookii]

It means you’ve got a reaction occurring between some of the elements in the mix, and forming a new compound which is beyond its solubility limit, so it precipitates out of solution as a solid.

Looking at the list, I’m not sure what it would be, so I’ll defer to someone with greater knowledge of chemistry such as @dw1305 or @X3NiTH

Long and short of it though, yes, your mix might be a bust, and won’t deliver the proportions of elements you planned.

 

[_Maq_]

4g PO4

?????

 

[MichaelJ]

Hello, i did a macro solution using :

• 4g PO4

@eminor, What compound is the "4 grams of PO4"? did you mean KH2PO4 ?


As for the residue, It might be with the quantities relative your your 808 ml of RO in the water bottle you have reached a solubility limit. Cut everything in half in your dosing bottle and just double the dose, makes sense?

Cheers,
Michael

 

[eminor]

@eminor, What compound is the "4 grams of PO4"? did you mean KH2PO4 ?


As for the residue, It might be with the quantities relative your your 808 ml of RO in the water bottle you have reached a solubility limit. Cut everything in half in your dosing bottle and just double the dose, makes sense?

Cheers,
Michael

yes KH2PO4. okay that will give more room to salt to dissolve, i'll try thanks.

Update : works great, so i reached the solubility limit, the precipit.. is gone, thanks =)

 

[_Maq_]

Nope. Since there's one and only cation in the blend - potassium - no solubility issue should have occured. I suspect your components contain some impurities.

 

[Happi]

Hello, i did a macro solution using :

• 808 ml of Ro Water
• 28g K2SO4
• 4g PO4
• 20g KNO3
• 32g KCL
• 6g Urea

I first added the ro water, then added salts in the order above, the hardest to dissolve to the easiest, there is a small amount of white powder on the bottom if i let it still ( 2 mm) , does that mean that the ferts are bad/ non effective ? thx

it kind of remind me of this #6 incident. are you sure those listed salts are exactly what you have used? are you sure its K2SO4 and not K2CO3? can you post a picture of the solution? I want to see how bad the Precipitation is.

only Ca can form CaSO4 in the solution, but the % is so small you wont even see it occur and it will likely get dissolved.

 

[eminor]

it kind of remind me of this #6 incident. are you sure those listed salts are exactly what you have used? are you sure its K2SO4 and not K2CO3? can you post a picture of the solution? I want to see how bad the Precipitation is.

only Ca can form CaSO4 in the solution, but the % is so small you wont even see it occur and it will likely get dissolved.
View attachment 201716

I though it was gone when i divided the concentration, seems there is still a dust of salt when i move it, barely visible but still there. The pictures show the main recipe.

I shaked it so much, doubt it could dissolve more than that. Could be wrong, but i though precipite get some color ? this looks like white/gray/transparent thing.

KH2PO4 is the only salt that i don't know the purity of it, i bought it from specialized tank website. Other salts are at least 99% pure exept urea which is 98 minimum.

 

[Happi]

I though it was gone when i divided the concentration, seems there is still a dust of salt when i move it, barely visible but still there. The pictures show the main recipe.

I shaked it so much, doubt it could dissolve more than that. Could be wrong, but i though precipite get some color ? this looks like white/gray/transparent thing.

KH2PO4 is the only salt that i don't know the purity of it, i bought it from specialized tank website. Other salts are at least 99% pure exept urea which is 98 minimum.

can you try making another solution using the same Ingredients and skip the Kh2PO4? and report back.

but i though precipite get some color ? this looks like white/gray/transparent thing

It depends on the Chemicals

 

[X3NiTH]

I would make the mix again without adding the Urea because it won’t be lab grade 99.999% pure, it’s going to be the compound with the most impurities. It doesn’t look like a carbonate precipitate because the sediment is not opaque and has transparency. It’s a lot of potassium salts going into solution and there may be a charge imbalance in the mixture and one or more compounds can’t fully go into solution.

 

[eminor]

thx guys, so i tried without urea, same result. Without KH2PO4 still have it. I once mixed KCL and other salt and it was ok, could be k2so4 ? but k2so4 is supposed to be 99.6% pure

 

[_Maq_]

It doesn’t look like a carbonate precipitate

Once again: There should be no carbonate precipitate because, among cations, there's only potassium present and potassium carbonate is pretty well soluble (as well as all potassium salts!). Ergo: impurities.

 

[eminor]

Once again: There should be no carbonate precipitate because, among cations, there's only potassium present and potassium carbonate is pretty well soluble (as well as all potassium salts!). Ergo: impurities.

Does the target ppm will be lower than expected then ?

 

[_Maq_]

Does the target ppm will be lower than expected then ?

Generally, yes, precipitates do not increase conductivity. Not very reliable, though, the more so if urea (non-polar solute) is present.