Precipitation

[hypnogogia]

I changed my diy mix today and the first time I made it I had precipitation when I added the magnesium sulphate.

my macro mix now is:
potassium nitrate
calcium nitrate
urea
monopotassium phosphate
magnesium sulphate.
as I said, the precipitation occurred when the magnesium was added. I’ve now added magnesium upfront and made the macro without it.

Was the reaction between the calcium nitrate and magnesium sulphate? Should I add the calcium nitrate to my micro mix to stop this from happening?

 

[plantnoobdude]

I changed my diy mix today and the first time I made it I had precipitation when I added the magnesium sulphate.

my macro mix now is:
potassium nitrate
calcium nitrate
urea
monopotassium phosphate
magnesium sulphate.
as I said, the precipitation occurred when the magnesium was added. I’ve now added magnesium upfront and made the macro without it.

Was the reaction between the calcium nitrate and magnesium sulphate? Should I add the calcium nitrate to my micro mix to stop this from happening?

Yes it's very likely the calcium nitrate and magnesium sulphate. You've got it right, just add it to micro.

 

[Hanuman]

@hypnogogia Any particular reason why you are using calcium nitrate for your nitrate source?
I personally like to keep any mix I make free of any calcium and simply dry dose it instead at water change.

 

[hypnogogia]

@Hanuman I wanted to reduce potassium.

@plantnoobdude thank you. Does it also react with mono potassium phosphate, or are the concentrations too low?

 

[plantnoobdude]

thank you. Does it also react with mono potassium phosphate, or are the concentrations too low?

Are you asking if it'll form calcium phosphate? I doubt it is very likely in our conditions.

 

[hypnogogia]

Are you asking if it'll form calcium phosphate? I doubt it is very likely in our conditions.

Yes, I read on a fertiliser website that calcium nitrate shouldn’t me mixed with sulphates and there’s a risk when mixing it with phosphates when making stock solutions.

 

[_Maq_]

Yes, calcium forms poorly soluble salts with sulfate and phosphate.
I gave up making blends long ago. Are you short of flasks in Oxfordshire?

 

[Hanuman]

@Hanuman I wanted to reduce potassium.

Can you provide the targets for each macro element?

 

[hypnogogia]

Yes, calcium forms poorly soluble salts with sulfate and phosphate.
I gave up making blends long ago. Are you short of flasks in Oxfordshire?

No, but I am short of dosing pumps.

 

[hypnogogia]

Can you provide the targets for each macro element?

NO3 = 30
K = 10
P04 = 3
Mg = 10
Fe = 0.5

I've tried some iterations on the fab calculator and see that I can achieve that without Calcium Nitrate, just using KNO3, Urea, Magnesium Sulphate and Monopotassium Phosphate.

 

[_Maq_]

No, but I am short of dosing pumps.

Ah yes. Laziness and love for fancy machines knows no limits.

 

[hypnogogia]

Ah yes. Laziness and love for fancy machines knows no limits.

Invaluable for folks who travel for work...

 

[_Maq_]

Magnesium Sulphate and Monopotassium Phosphate.

These can form precipitate, too, I'm afraid. But I've got no personal experience, in this case.

 

[hypnogogia]

These can form precipitate, too, I'm afraid. But I've got no personal experience, in this case.

are you saying it forms mono magnesium phosphate? This DIY is becoming a minefield.

 

[Hanuman]

I've tried some iterations on the fab calculator and see that I can achieve that without Calcium Nitrate, just using KNO3, Urea, Magnesium Sulphate and Monopotassium Phosphate.

I am not sure of the rational of doing 30ppm N03 and 10ppm K but under that scenario it becomes difficult to only use KNO3 and Urea and have your K on target. K can in fact be close to target which is ok but to that I have to point out that your urea should not be in the same amounts than KNO3, at least for starters. I would suggest lowering urea where it is only ~20% of your total nitrogen target. One way to mitigate this is to lower your NO3 and increase your K targets so that way you can increase NO3 ratio vs Urea. You might have to also use potassium sulphate to properly target K. Something like this for example. This is just and example of course and the dosing here don't matter.

Mg = 10

Something I am curious here. You say 10 ppm Mg. At those levels I am assuming you are using RO or rain water. If that's the case and assuming you are adding that magnesium in your macro bottle it would mean you are using your ferts to remineralize your water. If that is the intention I would advise against it and I would rather suggest you remineralize your water at WC dry dosing. The reason being that unless you are front loading, you wouldn't be remineralizing your water in one go but rather progressively during the week. Normally commercial fertilizers for planted tank contain marginal amounts of Mg and it's up to the user to remineralize the water at their desired levels (Mg and Ca) usually through dry dosing at WC. Also these commercial fertilizers assume your are using TAP water or some sort of water that has minerals in it hence why they add little Mg in it.

 

[Hanuman]

These can form precipitate, too, I'm afraid. But I've got no personal experience, in this case.

are you saying it forms mono magnesium phosphate? This DIY is becoming a minefield.

Never have I experienced (at least visually) any sort of precipitate forming when using both compounds together even where in some occasions I have used high levels of both in some fert mixes. I am not saying that chemically speaking nothing is happening, but I haven't see it with my eyes. There might be some reaction but to the extent of my knowledge and for our purposes I don't think it is relevant. In fact these two compounds are probably the staple in fert production, so no worries on that. Now what is true is that phosphate is like a magnet and tends to stick to anything and everything, even to your glass beaker when preparing a solution. That is why we don't usually mix phosphate with Fe because unless the water is properly acidified you will definitely see a reaction happen.

 

[hypnogogia]

@Hanuman I'm getting very confused now. Are you suggesting that for my macro, I use only:
KNO3, Urea (@20% of KNO3) and mono potassium phosphate. And then use the remineralising calculator to calculate the amount of Mg needed to get GH of 6, at a ratio of 3:1, Ca:Mg?

 

[hypnogogia]

Now what is true is that phosphate is like a magnet and tends to stick to anything and everything, even to your glass beaker when preparing a solution.

I've seen that happen.

 

[_Maq_]

I agree with @Hanuman. You can safely front load Ca and Mg because their amount regularly far exceeds plants' consumption. On the other hand, dosing potassium by small amounts should be helpful in keeping desired ratio: Ca > Mg > K.

 

[Hanuman]

I'm getting very confused now. Are you suggesting that for my macro, I use only:
KNO3, Urea (@20% of KNO3) and mono potassium phosphate.

20% of your total NO3/nitrogen target not KNO3. You can see in the screenshot above that the ratio of KNO3 to Urea is 4:1. In other words 80% KNO3 and 20% Urea. To be able to do that you would need to revise your NO3 and K targets and would probably need to also add potassium sulphate to properly target K. It's not advisable to go full bore with urea but rather go with small amounts and often.

And then use the remineralising calculator to calculate the amount of Mg needed to get GH of 6, at a ratio of 3:1, Ca:Mg?

Yes you can use the remineralising calculator for that as that calculator takes into account your WC volume rather the entire volume of the tank. It also allows you to tweaks things better as it allows you to target hardness and ratio which you can't do in the target calculator of the IFC calculator.