Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
As noted above, EC does not actually fertilize the plants. All the minerals it boasts about are actually locked up so tight the plants cannot get to them. Sort of like your dinner plate- you do not get your daily mineral needs because of your dinner plate. You have to add fertilizer to the tank the same way you put food on your plate.
On the other hand, if you need to add to the substrate for looks, or more root volume for the plants, you can do that.
Put the EC in a soda bottle, something with a narrow neck. Put the bottle in the tank and aim it toward the low spots. As the water enters the bottle and the substrate exits a lot of the debris will stay in the bottle. Probably a good idea to rinse it at least once before doing this, but I have seen some really impressive demonstrations with sand.