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Mold in DIY fertilizers with potassium sorbate

MrClockOff

MrClockOff

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Hello all
Hope everyone is doing well.
As said in the title I have noticed some green mould forming and floating on the surface of my NPK DIY fertiliser.
I have used IFC calculator to get the recipe. It states that I have to use 0.25gram of ascorbic acid and 0.2gram of potassium sorbate per 500ml of water.
I have used these Vitamin C Powder 100g - Ascorbic... https://www.amazon.co.uk/dp/B01JS2M0VM?ref=ppx_pop_mob_ap_share and Potassium Sorbate 100g for Wine... https://www.amazon.co.uk/dp/B07PFXZ7RG?ref=ppx_pop_mob_ap_share

Any good reason for this to happen or it’s just fake potassium sorbate?

Many thanks
 
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Well one of the issues making your own ferts is contamination. We are making a liquid broth the bugs of many types can thrive in, hence the reason the IFC advises you not to make ferts that last too long.
The best thing to do after making a bigger batch than will last 6 weeks is to split it up only using enough for four weeks and store the rest in a cool/dark place. I use fridge and freezer.
Also disinfecting your bottles and weighing equipment and auto feeding lines help.
Ideally we should be making the ferts in sterlie conditions.
Dosing dry ferts/salts is a better option if your tank is big enough and your dosing 5grams plus for each salt as weighing small masses is more prone to error
 
I had the same problem. I increased the Potassium Sorbate by 50% and I also added a small amount of Citric Acid. I can’t remember how much Citric I added but it wasn’t much. Since then I’ve not had a problem.
 
@Zeus. @Aqua sobriquet thank you for your comments. My batch is only prepared for 3 weeks and stored inside aquarium stand where is complete darkness.
I was surprised to find the mould after 3 weeks. I used to use Seachem Excel with great results but wanted to try something more neutral.
 
MrClockOff said:
My batch is only prepared for 3 weeks and stored inside aquarium stand where is complete darkness.
I was surprised to find the mould after 3 weeks
Click to expand...
That was quick to get mold. In the early days of hobby I use to make 5 litres at a time that lasted months but got mold in containers and auto dosing lines. Once I started using smaller volumes in active container and storing in freezer it was much less of an issue, auto dosing lines still needed flushing and disinfecting from time to time all the same
 
In present release of IFC the amount of E300 and E202 for a 500ml volume is
1718094946823.png


But in earlier releases of the IFC the amount was
1718095064913.png


Cant remember the good reason it was changed (@Hanuman might remember)
 
Hi all,
Aqua sobriquet said:
I increased the Potassium Sorbate by 50% and I also added a small amount of Citric Acid
Click to expand...
You can definitely add more volume acid, problems would only occur if you got to very low pH values. We know quite a lot about potassium sorbate (C6H7KO2), it is used as a preservative in foods - <"E202">.

Have a look at @X3NiTH 's comments <"Trace Elements/CSM + B, UK or Import - What do you use.">, it gives an explanation of what parameters are required for microbial growth.

cheers Darrel
 
Aqua sobriquet said:
Seeing Zeus’s clip it reminds me. I think I read somewhere about adding Acid to the water first so that’s what I did.
This is what’s left of a batch I made many months ago and it’s still nice and clear.

View attachment 220124
Click to expand...
Hence the promp in the masses to add to the water before adding other salts. Which was advised by @X3NiTH
 
As a matter of interest I wondered what the difference was between the two Acids I use in mine and found this online.

  1. Chemical Structure:
    • Citric acid is a tricarboxylic acid with the chemical formula C6H8O7. It has three carboxylic acid functional groups.
    • Ascorbic acid has the chemical formula C6H8O6. It is a six-carbon compound with a lactone ring structure and has ene-diol functionality.
 
Anecdotally, I never used potassium sorbate for my macro mix, and I still don't mix micros. I never had issues with mold. I did use boiling water in an attempt to reduce contamination.

One day I found a small package of potassium sorbate, thought it was cheap enough and decided to buy it, since that's what everyone is doing.

Next batch, I added 0.5mg/l to the macro mix and in less than 3 weeks I had green mold floating on the water for the first time.

I threw it all away and did it again, same thing. Still boiling the water. Again, mold.

Next batch I didn't use potassium sorbate, and it's been a month and no mold.

🤷‍♂️

I did mix an urea solution with potassium sorbate that is going well for a long time.
 
Hi all,
LMuhlen said:
I never used potassium sorbate for my macro mix
Click to expand...
You don't need to, it is actually the chelated elements in the trace element mix that provide the organic carbon (C) substrate for microbial growth.
LMuhlen said:
One day I found a small package of potassium sorbate, thought it was cheap enough and decided to buy it, since that's what everyone is doing. Next batch, I added 0.5mg/l to the macro mix and in less than 3 weeks I had green mold floating on the water for the first time
Click to expand...
The potassium sorbate would supply a carbon source (the formula is (C6H7KO2)), but you would need enough "contamination" by macro-element fertilisers to fulfill the <"assembly line aspect"> of microbial growth, this requirement is what @X3NiTH <"talks about">.

Plants, but still relevant
When I used to make up <"missing element"> hydroponic <"nutrient mixes"> for class experiments in plant growth, I found that none of the microelement deficient mixes worked (basically they all grew plants) and in the end I just told a "little white lie" and made up all of them (allegedly N, P, K, Ca etc. deficient) as magnesium (Mg) deficient mixes. If I did it now I'd also use some iron (Fe) deficient mixes (and possibly phosphate (PO4---) as well) to give a bit of variety.

Magnesium works perfectly, you get pretty instant greening and growth when it stops being Liebig's limiting nutrient.

You can just change <"nitrogen levels"> to effect growth and leaf colour <"The scientific background to the "Leaf Colour Chart"">.

cheers Darrel
 
Zeus. said:
In present release of IFC the amount of E300 and E202 for a 500ml volume is
View attachment 220118

But in earlier releases of the IFC the amount was
View attachment 220119

Cant remember the good reason it was changed (@Hanuman might remember)
Click to expand...
Might want to look at the logs tab dated May 24, 2022 (v1.2b1) of the IFC calculator.
I think the reason behind reducing the amount of E300 was because it was simply too much and unnecessary (although it doesn’t really hurt). Probably @X3NiTH told us so. Would need to double check.
 
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I never had mould forming in NPK or traces in 3 weeks batches. But because I never flush the auto doser I found black mould forming inside silicone tubes on NPK feed. Using Excel helped to clean the black mould.
I can see benefits of using ascorbic acid as it would help keeping chelates stable. But potassium sorbat looks like it won’t work for my intentions. Unless I am missing something here..
 
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