DIY Macro Solution Problems

Zeus.

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Hey guys
@Zeus. I managed to get it from a friend who is one of the distributors of chemicals and he lives near me.
However I just want to confirm if you think it's better to use the K3PO4 or just stick to the KH2PO4.?
I will again try to procure it from another seller and try the formula again.
Because using K3PO4 reduces the amount of sulfur added with the K2SO4.
Again I'm really sorry if this is all simple to you all but I'm really new at all this😁.
Thanks for all the replies.
Regards
Donovan
If the K3PO4 wasn't giving the ppt I would say its fine , however the ppt surgests IMO is impure. If we knew the impurity% or the K3PO4% of the salt was we could work with it. With it having a ppt ( we/you could decanter the soluble salt) the actual [K] and [PO4] will be less than you think, so A little more K3PO4 may be needed (if require). The beauty of using RO water is we know what's in the water as we have added it.
I would say using KHPO4 is better for most folk as it is easy to get hold off.
I don't personally have any issues with high SO4 levels as with my very hard tap water I dread to think how much SO4 s actually in the tap water, so I just accept it as it is as without going down the RO/rainwater route I have little choice ATM.
If/when I was using RO water I would use KCL and K2SO4 50:50 to help reduce the high [SO4].

Never apologize for asking a question, even if may seem simple/stupid to others :thumbup:
 

Donovan

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@Zeus. Thankyou for the reply.
Maybe like the batch of K2SO4 this batch of the K3PO4 is bad aswell.
However if I get a better batch I may try to make one with it.
I've bought alot of distilled water which I got really cheap so I have been using that.
If you add KCL and K2SO4 in a 50:50 ratio wouldn't the CL build up alot over time?
When I made my first batch i added K3PO4 and MgNO3 and this made the water completely milky. I mean it literally looked like milk.
Thanks for the replies
Regards
Donovan
 

Zeus.

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If you add KCL and K2SO4 in a 50:50 ratio wouldn't the CL build up alot over time?
Yes it would build up, however it would be limited by the weekly WC

When I made my first batch i added K3PO4 and MgNO3 and this made the water completely milky. I mean it literally looked like milk.

I take it you was using the MgNO3.6H20 which I believe is pretty soluble as well (can ne tricky to get data on as well), but to the ppt when mixing 'I dunno' @X3NiTH may be able to enlighten us on that mix.

I always have problems with dissolving salts too, always seem to have a little bit of white powder at the bottom. I never thought to change k2so4 supplier, i currently use aquaplant care salts.
https://aquaplantscare.uk/shop/aquatic-plants-fertiliser/k2so4/

I make a watered down mix too:
1000ml DI - 80ml doses
KNO3 22g
KH2PO4 5g
K2SO4 20g
again seems strange if the salt are pure
1604253746987.png

But if you mix your fert let it settle and decanter the clear liquid and use that then just watch your plants, if no signs of deficiencies, its a winner.

The calculator is a useful tool, but it doesn't replace watching your plants. Once you diagnosis a deficiency the calculator helps again as you can then increase the weekly dosing of the deficient element
 

X3NiTH

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If you are having precipitation where you shouldn’t it will likely be due to a compound that’s either there by accident or as part of the manufacturing process for the salt in question. If the resultant mixture has Charge Imbalance then depending on pH and temperature multiple different compounds can form and depending on the solubility rules can precipitate out of solution, in pure water alone oxides and hydroxides can form and even carbonates if the receiving solution is allowed dissolved atmospheric co2 in it.

Pourbaix diagrams are pretty excellent at conveying this information

Water -
1E68BB7E-2E87-4D33-92AC-2F3B00DCD7E7.png


CO2 -
1357647F-F832-4B4B-BE07-777EEECC07D8.png


Nitrogen -
80D0AE39-5324-4E6F-897A-715AE9D64B19.png

Some of the Micro Elements -
37A5187F-599C-4BED-A490-1D863432C62D.png

This last one shows that things can be a little different depending on the dilution of the sample.

At the end of the day if the mixture is built using compatible 99% pure salts and the 1% impurity forms a precipitatate then you are only losing a tiny amount of the total concentration so not worth even worrying, at less than 90% purity I would look for better. You can work out the percentage impurity of your salts by filtering off and drying the precipitate then weighing it to see how much you lost, (not really worth it unless your OCD).

Not sure I’ve been much help.
 

Donovan

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Hello everyone,
@X3NiTH extremely sorry for such a late reply.
Luckily I dont have OCD and that process looks to be very tedious so I wont go in for that. Haha.
However I solved the problem with the K2SO4 with a different supplier but I'm still having problems with the K2HPO4.
I sourced the K2HPO4 for a good supplier which says purity 99% and once again when I mix it with the magnesium sulphate or even magnesium nitrate it causes the liquid to become milky.
I get this same effect with the K3PO4 so I'm not really sure what the problem is.
This does not happen when I use just KH2PO4 and the KH2PO4 has a purity of just 98%.
Has anyone else faced this same problem or are the salts I'm sourcing just bad.

Regards
Donovan
 

X3NiTH

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I’ve posted on another thread recently where I mention the precipitation conditions for Potassium Magnesium Phosphate, I went and dug deeper to quantify what precipitation reactions happen with phosphate and Magnesium and I was unsure whether Magnesium had to be at saturation point in the water for precipitation to occur but from your description this doesn’t appear to be the case, the conditions for the above to form is that the solution will be above neutral pH and that the Potassium concentration exceeds the Phosphate concentration, the Phosphate concentration will be 3mM (miliMolar) or greater. 4.3g of KH2PO4 added to 1L of water is a 1mM solution (12.9g/L = 3mM). You don’t appear to be exceeding this condition but if you are adding all the salts together and then adding the water and it is above pH7 you will exceed these conditions as the salts dissolve in close proximity and as such precipitate will form.

Try to ensure your receiving water is void of any potential conflicting elements (0ppm TDS preferably) and acidify the water before adding the salts and dissolve fully the Phosphate first before adding the other elements (use the KH2PO4 as it reduces the overall K as you definitely have more K than PO4 in the recipe).

You could reduce the overall concentration of elements in solution and decrease the chance of precipitation by making a more dilute solution that you dose more of to the tank to reach your target levels.
 

Donovan

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Hello @X3NiTH
Thankyou for the reply.
I'm actually using distilled water so I don't have a problem with the TDS.
Also this perception only happens when I'm using the K2HPO4 or the K3PO4.
I dont not get any precipitate while using the KH2PO4.
In a 500ml container I'm adding
17.94 gms KNo3
7.89 gms K2HPO4
30.42 gms MGSO4.7H2O
12.01 gms KCL
20.72 gms K2SO4

I haven't acidify the solution prior to adding the salts however I do add one at a time and make sure its dissolved before adding the next salt.
I had mixed all the other salts and the last one was the MGSO4.7H2O and once I added this the whole solution turned Milky.
Maybe it did reach the saturation point.
I could maybe increase the KCL as it has a higher dissolving capacity than K2SO4 but I'm worried about increasing the CL concentration in the water.
Also I'm trying to keep it at 5ml per 100L cause I need the solution to last a but longer as i wont be at home for 4 months and my dad wont be able to figure the fertilizer calculations.
However as per the above mentioned quantities if you feel its not possible then I think I'll just have to make a very large batch and store that.
Regards
Donovan
 

Wookii

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Nottingham
Hello @X3NiTH
Thankyou for the reply.
I'm actually using distilled water so I don't have a problem with the TDS.
Also this perception only happens when I'm using the K2HPO4 or the K3PO4.
I dont not get any precipitate while using the KH2PO4.
In a 500ml container I'm adding
17.94 gms KNo3
7.89 gms K2HPO4
30.42 gms MGSO4.7H2O
12.01 gms KCL
20.72 gms K2SO4

I haven't acidify the solution prior to adding the salts however I do add one at a time and make sure its dissolved before adding the next salt.
I had mixed all the other salts and the last one was the MGSO4.7H2O and once I added this the whole solution turned Milky.
Maybe it did reach the saturation point.
I could maybe increase the KCL as it has a higher dissolving capacity than K2SO4 but I'm worried about increasing the CL concentration in the water.
Also I'm trying to keep it at 5ml per 100L cause I need the solution to last a but longer as i wont be at home for 4 months and my dad wont be able to figure the fertilizer calculations.
However as per the above mentioned quantities if you feel its not possible then I think I'll just have to make a very large batch and store that.
Regards
Donovan

Sorry if I'm stating the obvious, but if you're having solubility issues, why not just halve your salts per 500ml, double your dose to 10ml, and mix up two dosing containers instead of one, so you have enough to cover the period you are away?

EDIT: Or you could get a 1litre dosing bottle instead: eBay
 
Last edited:

Donovan

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Hello @Wookii
It isnt a solubility problem.
Actually I'm having a problem with mixing the magnesium sulphate with K2HPO4 or K3PO4.
I get a precipitation everytime I mix the MGSO4.7H2O with K2HPO4 or K3PO4. But this same issue doesnt arise when using KH2PO4.
So I wanted to know if anyone else has the same trouble.

Regards
Donovan
 

Zeus.

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It isnt a solubility problem.
Actually I'm having a problem with mixing the magnesium sulphate with K2HPO4 or K3PO4.
I get a precipitation everytime I mix the MGSO4.7H2O with K2HPO4 or K3PO4. But this same issue doesnt arise when using KH2PO4.

KHPO4 isnt as soluble as K2HPO4 or K3PO4 by factor of x4 so it doesn't initially point to a solubility issue IMO ( but I am not a chemist), points more to a interaction of the salts present. Is there a reason why you haven't added Ascorbic acid 1.0g/l and Potassium Sorbate 0.4g/l ?
 

Donovan

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Hello @Zeus.
Well I read on one of the posts that it isnt really required for the Macro solution.
However I will give it a try tomorrow and see if lowering the PH of the solution prior to adding the salts does make a difference.
I did a small test today with all the chemicals mixed separately in different containers and again there is no precipitation while using the KH2PO4 with other salts like K2SO4,KCL,MGSO4.7H2O,KNO3.
But again while using the K2HPO4 and the K3PO4 I get a milky solution.
The precipitate that occurs while using the K3PO4 is really thick and almost looks like glue settling to the bottom of the container.
All the salts are lab grade so I'm not sure what's going wrong.
Will trying the Ascorbic Acid tomorrow and hopefully it all goes well.

Regards
Donovan
 

Zeus.

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It doesn't take much to shift the equilibrium and before you know it you have a ppt, But you say it's like glue !!! which doesn't sound like a ppt to me.
I have always added the Ascorbic acid 1.0g/l and Potassium Sorbate 0.4g/l since I got mould in my first batch just to keep the 'fungi' in check. I was making 5 litre batches at first which lasted months, I do try to only mix 6 to 8 weeks worth nowadays
 

Donovan

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Hello
I'll try sending you a picture if it happens again after adding the ascorbic acid and potassium sorbate.
I'm sorry if I put that wrong about the glue. It's not sticky its it's just really thick and kind of heavy the precipitate which kind of looks like when you put a little glue into the water.
I will be making a batch now and hopefully it all goes well.
Thank you all for the hell.
Will let you'll know how it goes.😁
Regards
Donovan
 

Donovan

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Hello everyone!
So I even tried adding ascorbic acid and well it still results in a precipitation.
I've attached the pictures below while using the K3PO4 and K2HPO4.
I also tried making the solution with KH2PO4 and the soultion remained absolutely clear.
The K2HPO4 and K3PO4 both have a higher purity grade than the KH2PO4 but they both cause a precipitation.
I'm guessing I need to just get rid of the other two and just use the KH2PO4.
Even while using the same elements the reaction is completely different.

Regards
Donovan
 

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ian_m

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Right'o stretching my memory way back when investigating EI dosing years ago (2011 ?), why us fish peeps don't use tri-potassium and di-potassium phosphate, but stick to mono-potassium phosphate.

Basically the tri & di potassium phosphate have an issue to do with polymerisation under certain conditions and precipitate out of solution as polyphosphates especially under low pH situations. The polyphosphate is described as looking like "Elmers glue", which is US name for PVA glue. This matches what you are seeing.

Mono-potassium phosphate does not do this.

So yes you can dose, di & tri potassium phosphate but must be dosed separately to prevent polymerisation. Not sure what happens once in the tank, especially with low pH if using CO2, probably be OK as quite dilute.

In the end, I think mono-potassium phosphate is reasonably cheap, is one of the lower doses use in EI, so just dose this. Job done.
 

Donovan

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Hello @ian_m
Thankyou for the reply.
Like you said I'll just stick to mono potassium phosphate.
The only reason I tried to use the other two were to cut down the usage of K2SO4 and reduce the sulfur content building up in the aquarium.
How it looks to be too troublesome to use the other two.
Thankyou again.

Regards
Donovan
 

Zeus.

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Right'o stretching my memory way back when investigating EI dosing years ago (2011 ?), why us fish peeps don't use tri-potassium and di-potassium phosphate, but stick to mono-potassium phosphate.

Basically the tri & di potassium phosphate have an issue to do with polymerisation under certain conditions and precipitate out of solution as polyphosphates especially under low pH situations. The polyphosphate is described as looking like "Elmers glue", which is US name for PVA glue. This matches what you are seeing.

Mono-potassium phosphate does not do this.

So yes you can dose, di & tri potassium phosphate but must be dosed separately to prevent polymerisation. Not sure what happens once in the tank, especially with low pH if using CO2, probably be OK as quite dilute.

In the end, I think mono-potassium phosphate is reasonably cheap, is one of the lower doses use in EI, so just dose this. Job done.
Thanks for that Ian :thumbup:
and thats the reason why myself and @Hanuman decided not to add K2HPO4 and K3PO4 to the fert calculator 😇 or it is now 😂
 

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