DIY Fertilizer Formula Recommendation

[dw1305]

Hi all,

I am well equipped and take great care with chemicals.....but I think I went overboard on the strength. Thinking it twice I should have taken half strength (6 mol) as it will allow me easier control on PH.

@Hanuman. This is really important, don't open the bottles. These are potentially life threatening chemicals and should only be opened inside a fume hood, by a qualified chemist, who is wearing full protective clothing.

Breathing the fumes from the bottles will hospitalise you and if you try and dilute the acids in the wrong sequence you are likely to have an explosion.

cheers Darrel

 

[dw1305]

Hi all,

And what about sulfuric acid?

It's even more corrosive acid than HCl.

In any case is there a calculator out there what would allow me to calculate the ppm values that each of these acids add to the solution?

But why do you advise against it?

It is really because of your first question.

There are lot of different molarities of "hydrochloric acid", when we say HCl what we really have is an aqueous solution of the salt hydrogen chloride. Hydrogen chloride is really soluble, so concentrated HCl is twelve Molar, 37% HCl and a pretty scary liquid.

I know the dangers of strong acids. Beyond that aspect, is there any reason why not to use HCl.

Yes and no, even a dilute solution is still a strong acid, so you get a really rapid pH change <"when you run out of buffering">. You can see the titration curves below.



A weak acid is much safer.

cheers Darrel

 

[dw1305]

Hi all,

But think it's to do with HCL and H2So4 are simple acids so give up their H+ quite freely hence the big pH drop for given [molar], where as Citric acid is more complex so doesn't give up as many H+ as the simple acids at same [molar]. So when using simple acids you get bigger pH swings when added and as the H+ ions get mopped up, where as the complex acids give a small pH swing but as the H+ ions get mopped up the complex acids release more H+ ions due to the change in equilibrium so the complex acids have more buffering capacity- and help maintain a more stable pH, therefore better for tank

That is right. <"Strong" acids"> are acids that disassociate fully, so H+ and Cl-. "Weak" acids are "diprotic", so they have two disassociation constants.

This is the titration curve for when you add sodium hydroxide (NaOH) a strong base to ethanoic (acetic) acid (C2H4O2) a weak acid. Citric acid would give you a similar curve.



Weak acids can still be <"very strong corrosives">.

cheers Darrel

 

[X3NiTH]

Yikes! For relative safety I wouldn't have gone higher in acid concentration than a 1Molar Solution, you've exceeded that by quite a significant margin, definitely return them for weaker solutions, as Darrel says about the super high molarity acid and not having a fume hood 'Absolutely Do Not Open', the relative humidity in Thailand will go straight into the bottle and could start a fuming reaction and produce a lot of heat.

Using 1Molar HCl you need 1ml per 99ml of water (@pH7) to bring the pH down to 2.

If I absolutely needed product stability and long shelf life (unrefrigerated) I would still acidify the receiving water down to pH3 with Ascorbic Acid before adding the 1M HCl to bring it down the final point to pH2. This way you are not overdosing Ascorbic as the amount added for pH3 would still be advantageous to have in the mix for a little chelation, neither would you be adding too much Cl via the HCl.

I have given a bit of thought about which acids to use, (as above it would likely be combinatorial), HCl and Sulphuric for trace solutions only, either singularly or together to balance out the Cl and SO4 content in the final solution, can also can be used in Trace with the presence of Fe, if I didn't mind extra N you could use Nitric. Phosphoric I would use for 'All in One' solutions that already had PO4 in the mix. I wouldn't add Phosphoric to Trace+Iron just in case the P reacted with Fe in the bottle at some point through it's shelf life and dropped it out of solution.

 

[Hanuman]

Phosphoric I would use for 'All in One' solutions that already had PO4 in the mix. I wouldn't add Phosphoric to Trace+Iron just in case the P reacted with Fe in the bottle at some point through it's shelf life and dropped it out of solution.

Not sure I understand. You say you would use phosphoric acid for an all-in-one solution but not to a Trace+iron solution. An all-in-one solution contains Traces+iron so I am missing something here.

 

[X3NiTH]

Sorry that sentence reads a little funny. With an 'All in One' solution you would want N, P and K along with the Trace elements including Iron, so using an acid that provides N or P wouldn't matter since both these elements are required for this mix and could be used to supplement or replace a salt based source for these elements, it would be expected that in this mix Fe and P are going to be side by side in the bottle anyway and some amount of either will likely react and become unavailable, bringing the pH lower may make one or both these elements more available if the acid contains one of the elements needed.

If I were doing Trace and Iron only I wouldn't want to add a P based acid source because the mix doesn't require P.

It's the Hydrogen you want to move the pH, the corresponding element it comes with only matters if it reacts with some other desired element in the recipe making it unavailable.

Hopefully that makes better sense.

 

[Hanuman]

Sorry that sentence reads a little funny. With an 'All in One' solution you would want N, P and K along with the Trace elements including Iron, so using an acid that provides N or P wouldn't matter since both these elements are required for this mix and could be used to supplement or replace a salt based source for these elements, it would be expected that in this mix Fe and P are going to be side by side in the bottle anyway and some amount of either will likely react and become unavailable, bringing the pH lower may make one or both these elements more available if the acid contains one of the elements needed.

If I were doing Trace and Iron only I wouldn't want to add a P based acid source because the mix doesn't require P.

It's the Hydrogen you want to move the pH, the corresponding element it comes with only matters if it reacts with some other desired element in the recipe making it unavailable.

Hopefully that makes better sense.

It does. 🙂

To make things simple for an all-in-one solution I will stick to H3PO4 (Phosphoric Acid) as the "additional" PH reducer using C6H8O6 (Ascorbic Acid) as the initial PH reducer.

If preparing separate solutions perhaps sticking to C6H8O6 for the Traces should be enough. So far the separate solution of Traces I have made has been stable with only C6H8O6 for over a month. No precipitation observed. If I want longer shelf life or to combine Traces+Iron I might simply add a little HNO3 (Nitric Acid) or HCl or/and Sulfuric (H2SO4) as you suggested.

And promise I will exchange today those concentrated bottles of HCl and H2SO4 I have. I have to admit I got a bit carried away. This said, we are all here to learn and exchange so experimenting is important.

Hopefully this will appease some spirits. I do appreciate the concern though.

 

[Hanuman]

We good now?🙄

Couldn't find any lower concentration so will have to work with that.

I carried out some tests with plain RO water. Below are the results. I used a 2ml graduated pipette for the acids as well as a 1L graduated beakers for the water. The first 500ml of water for the first test were measured with a 100ml graduated cylinder (certified by the government - see pic below) for maximum precision. Repeated 5 times to get 500ml. I then visualized the level in the 500ml beaker for all other tests just to speed up things so there is probably a 5% +/- error margin in water levels for the following tests.

That sums it up. I took great care in handling those acids and happy to report I got no burns. I even had a sip of the phosphoric acid, was delicious. Nah just joking!

I suppose slightly less than 0.1ml of H3PO4 for 1L of water should work giving me a PH of 2.4. Of course this is without the addition of Ascorbic Acid so I am not sure if one would need to decrease the H3PO4 amount if adding C6H8O6.

 

[X3NiTH]

All good!

 

[Hanuman]

So if I am reading those TDS results right for H3PO4 I am getting 495ppm for 0.1ml of H3PO4 for 1L of water, which means 0.0495ppm of PO4 for a dosage of 1ml for 10L of water. Is that correct?

 

[Hanuman]

Hello all,

Would like to update and provide some feedback.

So I did some test batches today:

1 liter all-in-one: I used ascorbic acid + H3PO4. Strangely though, I was able to bring the PH down with the ascorbic acid alone to PH 2.6 with the prescribed quantity of 1g/1L. I pulled it further down to PH 2.2 with 13 drops of H3PO4. Not sure if that was in fact necessary though. So I started adding each trace one by one then mixing each time. PH went up to PH 2.8 after I finished adding all the traces. So far so good. Once I added the macros and then the Fe DTPA that is when things went south. PH shot up to 3.8 - PH 3.9. So that's not good. Since I did not test PH after adding the macros then it could have either been the macros or the iron or both. But I suspected the iron. So I did the following batch:

1 liter traces + iron only: this time I used ascorbic acide + HNO3 since I was not going to add macros. PH was down to PH 2.6 after adding the ascorbic acid. Adding 0.4ml of HNO3 brought the PH further down to PH 2.4. I then added the traces. PH went up to PH 3.2. This is the interesting part. I decided to stick my PH meter in the solution while adding half of the Fe DTPA. PH went right up to PH 3.8. I then added the remaining Fe DTPA. PH went further up to PH 4.1. Not good again.

So clearly the problem is my iron. And this is where it struck me. I am using Fe DTPA 7% and I need to add 21.43g/L to get to my 0.15ppm. Looking at Rotala Butterfly calculator only 13.64g/L is required with Fe DTPA 11%. So I might need to change my iron source.

@X3NiTH, @dw1305 what do you guys think?

 

[X3NiTH]

A while back I made up a concentrated solution of FeDTPA11% for dosing but never used it so it sat for months in the bottle, the sulphur came out of solution and formed a waxy in appearance sedimented cake on the bottom of the bottle that needing prodding to break the cake up to allow me to mix it back into solution, it always drops back out though again over time.

So extrapolating from the above observation in relation to the question then yes, using a higher percentage concentration of FeDTPA should lessen the pH rise to a degree, but it will always be there because the sulphate the iron is bound to alongside the DTPA drops the sulphur in solution thus freeing up a pile of extra oxygen to react with the extra hydrogen provided by the acid thus forming hydroxides which raises the pH. You would need to add more acid to counteract this effect.

 

[Hanuman]

So extrapolating from the above observation in relation to the question then yes, using a higher percentage concentration of FeDTPA should lessen the pH rise to a degree, but it will always be there because the sulphate the iron is bound to alongside the DTPA drops the sulphur in solution thus freeing up a pile of extra oxygen to react with the extra hydrogen provided by the acid thus forming hydroxides which raises the pH. You would need to add more acid to counteract this effect.

Thank you. I am currently sourcing some FeDTPA 11%. I think I found a source in Thailand. Will make new batches once I get it and share the results.

If I can avoid using stronger acids that would be great but I suspect there is no way around it because I still need to bring the PH down to PH2 in order to have a final solution in the 3 or 3.5 PH range. I tested the PH of a product called "Iron" from a company called Cal Aqua Labs. It was PH 3.4. In the past I used that company's product until I realized I could make my own. The products are good but just like any other liquid fertilizer making company for the aqua hobby, prices don't justify the content.

Interestingly when looking at your preparation your PH drops when you add the FeDTPA. Why would that be?

500ml Micro dosed @ 1ml/10L, Preparation as follows -

450ml RO/DI + 0.25g Ascorbic Acid - pH 3.2

+ 0.77g MnSO4.H2O (Mn 0.05 mg/L) - pH 3.42

+ 0.9g ZnSO4.7H2O (Zn 0.04 mg/L) - pH 3.5

+ 0.86g H3BO3 (B 0.03 mg/L) - pH 3.5

+ 0.019g Na2MoO4.2H2O (Mo 0.0015 mg/L) - pH 3.6

+ 0.04g CuSO4.5H2O (Cu 0.002 mg/L) - pH 3.68

+ 0.0113g NiSO4.6H2O (Ni 0.0005 mg/L) - pH 3.74

At this point the resulting mixture is clear with zero precipitation. The addition of the Fe increases the opacity of the mixture.

+ 50ml Fe Gluconate (pH 3.05 - Fe 0.1 mg/L) - pH 3.35 (Green tint to the mix)

+ 2.275g FeDTPA 11% (Fe 0.05mg/L) - pH 3.19 (Brown Green tint to the mix)

 

[X3NiTH]

The pH of my concentrated FeDTPA solution that I talk about above has an equilibrium pH of 3 (I just tested it, yup it's still in the bottle with its sulphur sediment). If you make up a concentrated solution of your own source you will probably find the pH is much higher because there's is more sulphate being added in 7% concentration Fe than 11%, all that extra sulphate provides the extra oxygen to bind with the hydrogen and form hydroxide raising the pH.

You can see in my mix that every time a sulphate is added there is a corresponding rise in pH due to the extra O₄ being added thus reacting with the Hydrogen and forming hydroxide bumping up the pH. When I add the FeGluconate more hydrogen is being added so the equilibrium changes and the pH drops, because the pH of my 11% FeDTPA is lower still there is a corresponding further drop.

So your initial assumption is correct, the pH difference is due to the lower concentration of Fe in the 7% than 11% requiring a significantly larger volume of carrier to be added (SO₄) to attain the same Fe mg/L values as 11% concentration.

 

[Hanuman]

Thank you for explaining the details. I have ordered FeDTPA 11% and should be getting it this week. See attached PDF for info on the product.

As for the all-in-one that I prepared the other day, as expected, some reaction occurred. I checked this morning and there was a sediment layer at the bottom of the bottle. I guess I will be using that batch to fertilize my plants outside!

 

[Zeus.]

A while back I made up a concentrated solution of FeDTPA11% for dosing

What concentration did you make m8? ( if you can remember) Could this precipitation have a concentration threshold ? or is it just a case of once the the O2 gets in solution we have slow breakdown.

 

[X3NiTH]

I thumbed through my notes and found a page with zero context, it can be decoded with access to my personal computation unit and the cypher 1ml/50L.



The cryptic Vape potion reference is the container size I had to hand of 60ml. The target dose would have been 1ml for 0.15mg/L Fe in 50L, the DosingBottle reference is the concentrate premixed in a 60ml bottle (empty vape juice container, unused and of the same type the Mangabeys vape juice potion comes in, hence the cryptic reference).

Total Fe in the 60ml concentrate is 6,480mg, that’s the Fe weight for FeDTPA11%, if you add the other 89% of gubbins you get the total weight of the salt added to that 60ml potion bottle to make the dense concentrate mentioned above!

🙂