I been using the Osmocote Flower and vegetable formula for a few year's now.
My tanks are soil based and I sprinkle the tiny pellet's on the glass or thin layer of soil before covering with more soil and then capping the soil.
Last month I re-dirted my 80 gal tank in this way and used about a half cup of the osmocote sprinkled on the bottom as mentioned,and then a half cup of Green sand soil amendment,followed by the soil, and capped it all with product safe-t -sorb.
Has only been three week's but the few cherry shrimp and a couple of old female swordtail's are doing fine along with the plant's (sword's,crypt's,anubia)
Agree with other's ,a little of the osmocote goes a long way and is maybe not for those who uproot or move plant's about frequently.