Is my Iron DTPA solution precipitating or growing a film?

[_Maq_]

Correct me if I'm wrong, but isn't there acetic acid in DTPA?

free from unnecessary retorts regarding semantics.

You asked for it - you got it.

 

[MusciViridis]

You asked for it - you got it.

Is it truly widespread? Is it widespread in combination namely with DTPA? (Because "chelated iron" does not indicate that all compounds containing iron in coordinate bond are chemically similar!) Is it really necessary? And, generally speaking, is "widespread" equal to "desirable" or "beneficial"?
@Disaronno and @Happi suggested potassium sorbate. @John q suggested no additives. Me, I consider both these suggestions better than acetic acid ... excuse me, vinegar.

I didn't ask for this. 😑
But sure, continue sharing whatever makes you feel superior.✌️

 

[Hanuman]

This is my second time making my own Iron DTPA solution and it seems to have precipitated or started growing film suspended in the solution. I threw out the first batch after it started developing the film over several weeks. I made a new one last week and started seeing precipitation/ film after a week. Before making the second batch, I rinsed out the pump bottle with tap water and then with distilled water to prevent this from happening again to no avail. Here's my current procedure:

1. Warm up 250 mL of distilled water in the microwave.
2. Stir in 5 mL of distilled white vinegar (to bring down pH and prevent precipitation in solution).
3. Let the solution sit for a minute.
4. Mix in Fe DTPA 11% powder.
5. Stir until completely dissolved.
6. Pour into a blue opaque pump bottle.
7. Stir it a few more times and let it sit until cool.

I'm seeking guidance on whether there might be an error in my procedure or any preventive measures I can take to avoid this issue from recurring. Any suggestions would be greatly appreciated.

Film and precipitation are two very different things. What you show on the picture is mold, not precipitation which would be very odd considering you are only adding Fe DTPA in there. Precipitation will most of the time settle at the bottom of the bottle as dust since the precipitate is denser than water.

Overall, your procedure is fine and others have already recommended a few tweaks. The heating up and acid addition are unnecessary though, unless you would be adding multiple compounds or doing an AIO solution where the PH could potentially rise to the point where certain compounds could start interacting. FE DTPA 11% usually remains stable between a PH of 4 - 7.5. Outside that range it could degrade so over-acidifying your water could have a negative effect on the compound. Since Fe-DTPA self-acidifies the water to PH 4 then it is not required to add any additional acids.

Some have stated that heating up the water is not required and I agree as Fe DTPA will fully dissolve without that step. This said, I do boil the water myself for a good 5 minutes to remove any potential lingering germs. The cleaner your vessel is and anything that comes in contact with the solution, the least amount of mold formation you may have.