Ascorbic Acid, Humic Acid, Fulvic Acid and Tannic Acid are all natural biodegradable Chelates, when it comes to molecule size Tannic Acid is a monster, if it scavenges Iron the molecule becomes opaque black (this is what Iron Gall drawing ink is, Iron Tannate), I have no idea about whether a plant can utilise this.
Does that mean you wouldn’t recommend adding those organic acids to a micro mix?