Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Fertilizer tablets are available. Press them into the substrate, do not turn them loose in the water column. You can also make your own from pottery clay and the dry ferts.
If you want to use the fish feeder idea, can you make sure they won't mix, and put the Macros in every other day, and the Micros the alternate days? Dropping these directly into the tank is not a problem.