I made some clay plug's with osmocote prill's inside, and then let em dry in the sun for a day or two.
I was quite pleased until,,, I tore down the tank about six month's later only to discover that the clay plug's I had made were still very much intact and I had doubt's at that time that they were very effective at all.
In fact ,that was why I tore down the tank to create better substrate due to lackluster growth.
I resorted to filling ice tray with water and sprinkling osmocote in the tray's and then freezing them.
Worked much better!(push em down deep and quick)
Believe there are a couple member's here that make em from gel cap's filled with osmocote.