Ferrous gluconate stability

Hi Rodrigo! Welcome!

Ferrous gluconate is not as stable as iron chelated to EDTA or DTPA. Gluconate form of iron is available to the plants for a while, but then it precipitates.

However, gluconate is very well absorbed by the plants when it is present in the water. It is probably preferred by the plants because it requires less work and energy to access the iron in Glucoante than in EDTA and DTPA. Most of us who have played around with various form of iron eventually figure out that a combination of Gluconate and DTPA works best.

Don't worry about the lack of stability of Gluconate. This just means that you may need to dose a little more iron if dosed as Gluconate.

 

Mostly will depend on the PH of the water you use to make the solution. Adding 5 ml of distilled vinegar to 500 ML should keep it stable. Citric acid works too, vinegar is easier.

 

Excel is ok if you're worried about mold but it doesnt get the PH/KH down, which to my knowledge is the primary factor in gluconate (and other micro elements) being stable.

Unless something has changed recently, Tom uses tap water + vinegar for his micros, along with gluconate as a small part of his Fe

I use distilled water + vinegar for my custom blend, it contains all the same micro elements that are in Flourish Comp + Fe gluconate + Fe DTPA.. I dont keep it refrigerated and have never seen any mold or precipitation, weird color change, etc.

It stays crystal clear and the exact same color. But I have also not keep many mixes over 3 months either.

I dont know what Seachem uses as the base water or to stabilize the PH, but Im pretty sure they just dont want people who keep it for a very long time getting mold is why they say to refrigerate after 3 months.

Excel obviously kills/prevents bacteria, but it's doesnt have an indefinite shelf life either (might be another reason they say refrigerate after 3 months).

As for the possibility of fermentation I really have no idea

 

I rage through Trace mixes every 2 weeks or so. So nothing last too long. You can add both, vinegar 1st, shake good in hot tap water, this destroys the KH............then add the Trace mix you want..............then some Excel at the end.
For auto dosing of 20 liter vats, I just make them 1/2 strength 0.75% Glut and add the macros and the traces to two large containers, then dose daily. Harder dKH's, I'll use CMS and DTPA, lower dKH tap water/tank water..............I'll add some Fe Gluconate. I will generally use HCl for the larger vats, I'll use the pool acid 23%, adding about 10-20 mls per liter 1st, then wait a few minutes, then the traces.

You can mix better with with hot water, so if possible, mix with that, then the acid, wait and shake a bit, then the trace mix, and shake and mix good.
Some have used potassium sorbate, a common food preservative.

Generally, most acids work well, but 5% distilled vinegar is safe and cheap, and .......available.
It pickles things for years.