It is a very thin and even layer in a solid matte white color. Definitely not like powder-like, chalky or moldy.
This is definitely some kind of precipitation happening, for sure. With micro mixes, this can occur if you're adding all the salts at once to the solution. That precipitation might affect the dosing, it might not, but you definitely need to use mixers or hand-mixing before dosing. The problem with auto dosers after stir bar mixing, is that the precipitate will likely still form and fall out in the tubing itself so you don't get properly homogenized dosing.
So you don't use any vinegar or ascorbic acid next to potassium sorbate? Does it still get acidic enough?
I've been mixing my own micros solution for about 2 years now and I never add ascorbic acid. Definitely don't need the KSorbate, these mixes are concentrated in things that are mold inhibitors on their own. You're not getting mold, you're getting precipitation!
These are the salt I will use:
- Fe 13.2% EDTA
- Manganese Sulfate Monohydrate (MnSO₄·H₂O)
- Zinc Sulfate Heptahydrate (ZnSO₄∙7H₂O)
- Boric Acid (H₃BO₃)
- Copper Sulfate Pentahydrate (CuSO₄∙5H₂O)
- Ammonium Molybdate Tetrahydrate ((NH₄)₆Mo₇O₂₄∙4H₂O)
- Nickel Sulfate Hexahydrate (NiSO₄∙6H₂O)
When I first started making my own micro mixes, they got precipitation. I'd weigh all of the salts, dump them into a small tray, and add it all to my ~400mL beaker for mixing until dissolved. Then, top off to 500mL.
It would be a bit cloudy, get better, and look ok that day, but precipitate out over the next few hours/days.
Here's what fixed my precipitation issues: Mixing order!
First, you'll likely need to make secondary solutions for your Cu, Mo, and Ni. I'd find some airtight containers, and make secondary solutions of these salts first. Normally I don't promote AI use, but this is a use case where it makes sense. It'll help you out. I like to use 250mL media glass bottles for three separate Cu, Mo, and Ni solutions that'll last me a lifetime. Get a 1mL syringe, 5mL syringe, or 10mL syringe for dosing and adding these to your main mix when it's time.
Once your secondary solutions are made,
here's the proper mixing order (I have this memorized now lol)
:
- Fe EDTA (I recommend DTPA 11% over EDTA, but use it if it's what you have). Mix until fully dissolved.
- Boric Acid, mix until dissolved
- MnSO4, mix until dissolved
- ZnSO4, mix until dissolved
- Add Cu stock
- Add Ni stock
- Add Mo stock
- Mix well, top off to your desired volume. Make sure you're always using RO water or distilled water, not tap.
I do this all with actual graduated cylinders, with a stir bar in the bottom, and RO water heated to ~120F.
Once you make those secondary solutions, you'll only be removing a few syringes'worth (if that) each time you make your micros, so it's totally worth it. We make secondary solutions because none of us have scales that will accurately weight 0.00067g of something...
I follow
@Burr740's micro recipe, where for every
0.01ppm Fe added, it also adds about:
Mn - 0.0017 ppm
Zn - 0.0017 ppm
B - 0.0015 ppm
Cu - 0.00014 ppm
Mo - 0.00007 ppm
Ni - 0.00001 ppm
I start with my DTPA 11%, then boric acid, then Mn, Zn, then my Cu/Mo/Ni secondary solutions.
Previously when I added all powders together, it would preciptate -- over and over and over again.
Including a mixing order finally gave me a totally clear micros solution. No acid (besides boric acid), no KSorbate!
Let me know if you have any questions!
Sodium Na+ is a cation so it would your soil would bind up sodium over time, competing with potassium calcium and magnesium at the root-soil interface, as well as aggravating plant-specific specific sodium toxicity. This is one reason a hallmark of sodium toxicity is a lack of rooting 
He has replaced with an inert soil, so the cost was much more reasonable than the new Aqua soil 
Even with a magnetic stir bar and stir plate, it still doesn't dissolve quick enough for me. I want to make my micros mix in 30 minutes or less, and have it last for a few months if possible!
