I read a long time ago that Humic/Fulvic acids make silica available for uptake. Can't remember where, but I found this.
I also use them to neutralize chloramines in tap water.
"The Fulvic Dissolver
Fulvic acid has a unique capacity to dissolve insoluble materials. Research suggests that iron, a poorly transported mineral, essential for all plant life, is dissolved, complexed and transported into the plant much more efficiently in the presence of this organic acid. A low-molecular weight piggyback ensures easy access and improved translocation of the iron cation.
Fulvic acid also solubilises potassium. Potassium is the most expensive of the minerals from a fertilising perspective, but large reserves are present, in insoluble form, in all but the lightest of soils. Potassium released by the ‘fulvic dissolver’ will reduce fertilising costs.
Silica is the flavour of the month in soil science circles. Fulvic acid has a particularly strong solubilising potential for silica. Water-soluble silica performs a similar role to calcium, strengthening cell walls and building brix levels.
Research also confirms enhanced phosphate solubility and stability, but silica, potassium and phosphate are all more susceptible to fulvic solubilisation in the presence of iron. Fulvic acid has an affinity for iron and can actually transport three to ten times its own weight of this metal. The mineral products most susceptible to disintegration by fulvic acid are those that contain the highest percentage of iron. NTS Soft Rock ™ contains phosphorous (10%), silica (25%) and iron (2%)*. The solubility of this product could definitely be enhanced by fulvic acid. Rock dust also contains good iron levels, and most rock mineral fertilisers will perform better with fulvic acid.
*These percentages may vary. Please refer to Product Information Sheet for up to date analysis."