Have you tried to put few worms right in the aquaponic system, on the clay balls? I remember reading a while back about someone who made a video showing compost worms feed off the deposit on the clay balls, cleaning them and releasing compost directly for the plants.
Yes, I've put a handful into each bed after the beds were well established. I often find one when I'm removing or replacing plants so they're doing quite well after a year.
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