How to break down fish solids within the bio filter

I'm fairly new to aquaponics.  My current design is a self contained vertical tower.  I seek all information that can break down fish solids into plant food. Thus eliminating the need for removal. Normal practice by backyard aquaponists is to remove the solids to their dirt garden.  (plant food) right? My solids separator is within the tower where no part of it is ever completely submerged. But at the thickest part of the cone shape filter is always moist. I'm trying to simulate the dirt garden process into aquaponic.  I don't expect a solution, just some related documentation which may help find the solution.
Thanks