Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
There is no aquarium osmocote. Look for osmocote plus in any garden center, including the stores you mentioned.
00 gelcaps are a medical thing, easily available on line. Fill them with osmocote and push them under the substrate.
Freezing as described above is a good way, too.
There is not enough copper or other nutrients in osmocote to cause problems in the aquarium. First of all, you are not using very much. Second of all it is slow release, so all the minerals etc that are in the osmocote are released slowly, so the plants use almost all of them.