Substrate micro injection

Has anyone injected ferts in their substrate? Root tab user found a new tablet. The tab was an over the counter gel cap filled with micro nutrients, red clay powder, and others. Basically its the same mix as what dirted tank enthusiasts lay down before the dirt, and or "mineralize" their dirted substrates.
Anyway, the gel cap would stick to my fingers before I could push it into the substrate.

Armed with a fat syringe (ear cleaner) I opened a few gel caps, mixed the contents with hot water mixing as much as i could so it wasn't lumpy. I had to drill a bigger hole in the syringe because the red clay powder won't actually dissolve and it plugged it up.

So, starting with just a few plants i was able to inject the contents right into the substrate. I was impressed due to the fact i was able to angle in and get right into/under the roots of established plants. With bulky root tabs you can get close but its hard to get under without worrying about disrupting. Also there is no replacing root tabs in a closely planted tank without disrupting substrate, plants, and such.
Injecting the solution was very simple, and absolutely no disruption of the aquscape. *thumbs up!

A few weeks later i would could tell a difference in health , fullness, and overall growth in the plants.

My substrate is a mix of 6 year old black fluorite gravel, sand, and eco complete. Has anyone else done anything like this?