I'm setting up a new Aquaponic system, kit bought, has 2 grow beds with a bell siphon that sit on a small fish tank with a continuously running pump. Beds filled with expanded clay, tank filled with gold fish.

The plants I've been using are established from soil, about 5-6cm of plant and about the same of roots.

I've been running for a couple weeks, and I am having an issue with my plants rising to the top and laying on top of the clay pebbles.

Some plants have died, some I've been able to make a hole and basically replant and are still surviving.

Is this a common issue or am I missing something?

I thought of trying a base of clay pebbles and the rest of a coco perlite mix (might not shift as much with the flood) but I hear it stores a lot more water and might not be appropriate with a siphon flood and drain system.