Media filled beds are the simplest form of aquaponics, they use containers filled with a suitable growing media such as hydroton (expanded clay balls), pumice stone, gravel or something similar. Water from a fish tank is pumped over the media filled beds and plants grow in the rock media.
This style of system can be run two different ways, with a continuous flow of water over the rocks, or by flooding and draining the grow bed in a 'flood and drain' or 'ebb and flow' cycle. The growbeds should be about 12" in depth as this has been proven to be the most effective depth for plant growth and the cultivation of a beneficial eco-system in the beds.
Once the water reaches the appropriate level then the water will be drained from the growbed (usually quickly) which will draw oxygen back down into the growbed for the benefit of the plants and microbes.
This cycle then continues regularly and provides the plants with all of the nutrients that they need to grow extremely abundantly and naturally without any added pesticides, herbicides or fertilisers.