Vinegar or Citric Acid to lower pH of All-in-one fert mix

[Djoko Sauza]

Which acid is most appropriate for acidifying a fert solution? For reference I make a 420ml batch with RO water and dry salts and it lasts me 2 weeks.

Last time I used white vinegar and the solution got cloudy towards the end. Could this be from the vinegar? Or is it from the solution not being acid enough and stuff precipitating? It has happened a few other times before, but not always.

Just made a new mix today with Citric Acid instead so we'll see how things go. I added 2grams of Citric Acid to the 420ml of RO water.

Ideally I want to make the solution last up to a month in the cabinet, has anyone achieved this?

 

[zozo]

What is used in the botanical trade for acidifying fert solutions depends on what is grown and the seasonal properties of the plant. For example, flowering and fruit carrying plants benefit from extra phosphor during the flowering season. Then the fert solution will preferably be acidified with phosphoric acid (H3PO4) to give a tad extra phosphor.

For plants during the vegetative season ore plants that don't flower or are harvested before they do benefit from extra Nitrate then Nitric acid (HNO₃) is used to give that extra Nitrate.

How it acidifies the tap water is highly dependent on the water parameters and its buffering capacity, water with higher carbonate content neutralizes acid rather quickly in a matter of hours. Then what you'll experience are pH swings, going down and up again when all is neutralized. Thus it's buffering the acid to a point when it's saturated. Initially, you could need quite a lot of acid to lower it 1 pH unit, but the water buffers it and it will go up again. If you like to correct it after that you would need significantly less acid and there it becomes tricky. If you add too much and that could be very little acid while the water is (almost) saturated then the pH will crash significantly below a safe value. For that reason playing with acids to lower/regulate pH in an aquarium is not really recommended it's a tad like playing with fire.

In an aquarium Vinegar as well as citric acid could be used without any ill effects in some cases it mighty benefits plant growth. But be warned the Ph crash could be around the corner with 2 drops of too much acid..

For the fert solution itself, anything acid is also a preservative... I'm not sure if and why one should be better than the other.

Stuff precipitating likely is the reaction with calcium carbonates in the solution, which is one of the buffering agents reacting with the acid. I'm not a chemist but there are likely also other elements doing this depending on the concentrations. And fert solutions are dissolved salts in water also this can precipitate. The shake well before used on the bottle is for that...

 

[Djoko Sauza]

What is used in the botanical trade for acidifying fert solutions depends on what is grown and the seasonal properties of the plant. For example, flowering and fruit carrying plants benefit from extra phosphor during the flowering season. Then the fert solution will preferably be acidified with phosphoric acid (H3PO4) to give a tad extra phosphor.

For plants during the vegetative season ore plants that don't flower or are harvested before they do benefit from extra Nitrate then Nitric acid (HNO₃) is used to give that extra Nitrate.

How it acidifies the tap water is highly dependent on the water parameters and its buffering capacity, water with higher carbonate content neutralizes acid rather quickly in a matter of hours. Then what you'll experience are pH swings, going down and up again when all is neutralized. Thus it's buffering the acid to a point when it's saturated. Initially, you could need quite a lot of acid to lower it 1 pH unit, but the water buffers it and it will go up again. If you like to correct it after that you would need significantly less acid and there it becomes tricky. If you add too much and that could be very little acid while the water is (almost) saturated then the pH will crash significantly below a safe value. For that reason playing with acids to lower/regulate pH in an aquarium is not really recommended it's a tad like playing with fire.

In an aquarium Vinegar as well as citric acid could be used without any ill effects in some cases it mighty benefits plant growth. But be warned the Ph crash could be around the corner with 2 drops of too much acid..

For the fert solution itself, anything acid is also a preservative... I'm not sure if and why one should be better than the other.

Stuff precipitating likely is the reaction with calcium carbonates in the solution, which is one of the buffering agents reacting with the acid. I'm not a chemist but there are likely also other elements doing this depending on the concentrations. And fert solutions are dissolved salts in water also this can precipitate. The shake well before used on the bottle is for that...

Thanks for the reply. Just to make it clear, I'm not adding acid to lower the aquarium water pH. I'm trying to keep the fert solution below 6 pH so that phosphate and iron don't mix and become unavailable for plants to uptake (or something like that, yeah I'm not a chemist).

I'm adding to RO water:
KNO3
Urea
KH2PO4
K2SO4
Mg
Micro mix including Fe EDTA
Citric acid (or vinegar)
E202

So there shouldn't be any calcium carbonates present.

My issue is the solution going cloudy, the goal is to have it last as long as possible. Perhaps the acidifying agent is not even the issue here.

Just wondering how others manage to keep their AIO ferts good for a long period of time in a non refrigerated place.

 

[Happi]

@Diogo Sousa
I do not recommend using RO water to make fertilizer solution, instead use Distilled water. I use 10 ml Vinegar in my 500 ml solution along with 0.25 - 0.5 gram Potassium sorbate and this should keep the solution from precipitating, sometime I use Sodium Benzoate for replacement for Potassium Sorbate. these solution are kept in the room temp in the dark, some are still good even after 1 year. it seems like DTPA Chelated one seems to last even longer. I see more precipitation at the bottom when I used Vitamin C (Ascorbic acid), it can potentially react with Copper in the solution. even Mg and PO4 can react with reach other but this is rarely seen in the solution that we make. have you tried making the solution without Ascorbic acid or K2SO4 added to the solution?

most people don't know this but K2SO4 can also add bit of Calcium but this number is so minimum that it shouldn't have a major effect on the solution.

​

 

[zozo]

Thanks for the reply. Just to make it clear, I'm not adding acid to lower the aquarium water pH. I'm trying to keep the fert solution below 6 pH so that phosphate and iron don't mix and become unavailable for plants to uptake (or something like that, yeah I'm not a chemist).

I'm adding to RO water:
KNO3
Urea
KH2PO4
K2SO4
Mg
Micro mix including Fe EDTA
Citric acid (or vinegar)
E202

So there shouldn't be any calcium carbonates present.

My issue is the solution going cloudy, the goal is to have it last as long as possible. Perhaps the acidifying agent is not even the issue here.

Just wondering how others manage to keep their AIO ferts good for a long period of time in a non refrigerated place.

Ok, then I misunderstood or did misread your post... When I was about done writing it dawned to me that your goal might be preserving a mixed solution...
There are a few threads about here at UKAPS... If you search the forum for Ascorbic Acid (also used for this purpose) you'll find a few threads... I know @Zeus. and @ian_m do auto dosing and knows stuff about preserving fert solutions.

 

[X3NiTH]

2grams of Citric Acid to the 420ml of RO water

You only need 0.5g/L to reduce RO/DI pH to 3.25. Acidify the receiving solution first before addition of elements, add the phosphate first and then test the pH, add more acid to reduce the new solution to a pH around 4 or below (aim well below the pH required to break the bond on the iron chelate in use). Add the rest of the Macro elements including the preservative and ensure full dissolution so there are no undissolved compounds or precipitate, you can then add the Micro Elements and Iron Chelates, mix vigorously until fully dissolved, leave the mix to sit in a cool dark place for a couple of hours and check for precipitation, if everything went according to plan the mixture should remain clear. Keep refrigerated for longevity and dispense amounts to use that don’t sit for months at room temperature reducing the chances of inevitably growing fertiliser Kombucha despite preservation.

 

[Djoko Sauza]

You only need 0.5g/L to reduce RO/DI pH to 3.25. Acidify the receiving solution first before addition of elements, add the phosphate first and then test the pH, add more acid to reduce the new solution to a pH around 4 or below (aim well below the pH required to break the bond on the iron chelate in use). Add the rest of the Macro elements including the preservative and ensure full dissolution so there are no undissolved compounds or precipitate, you can then add the Micro Elements and Iron Chelates, mix vigorously until fully dissolved, leave the mix to sit in a cool dark place for a couple of hours and check for precipitation, if everything went according to plan the mixture should remain clear. Keep refrigerated for longevity and dispense amounts to use that don’t sit for months at room temperature reducing the chances of inevitably growing fertiliser Kombucha despite preservation.

To be honest I used 2 grams of Citric Acid because I looked at it and thought "this ought to be enough!", as stated before I am no chemist ahah. Amazing that as little as 0.5g/L lowers the pH so much.

Why would the pH raise when adding phosphates?

A bit off topic but does anyone know a tool to check how much salts we can add before the water gets saturated and they can't dissolve anymore? Does it work per compound or per total ppm of added salts?

Thanks for all the helpful replies until now!

 

[dw1305]

Hi all,

Does it work per compound or per total ppm of added salts?

Total ppm of <"added salts">. <"The IFC calculator has solubility limits built in">.

cheers Darrel