In the life of every aquaponian comes the day to wash media to go in the growbeds. We decided on a two layer approach though we know the layers will become somewhat mixed over time.
Our first and bottom layer is hydroton. Hydroton is pelletized, fired clay and is manufactured in Germany. The pellets will hold up over time and are very porous. This provides a good home for bacteria to develop and thrive. We purchased 4 bags from a local hydroponics store called Everybody's Garden Center. They had the best price we could find either locally or on the internet. Once home and washed, the hydroton filled up about 3 inches of the overall 10-11 inches of media for the beds.
Update: In future systems, we would not use the hydroton in connection with gravel. Hydroton makes sense for a system where weight is a consideration since it is much lighter than gravel. But to create a layer at the bottom of a gravel bed, it is wasted effort. The gravel and hydroton mix together over time. The original theory was to provide an excellent surface for bacterial growth. Gravel is sufficient.
The remainder of each bed was filled with pea gravel. We went to the local garden center and inspected their product and felt comfortable with the size. From our research, we had learned that around 8-10mm or around 1/3" size is best. When we got home and started washing, we realized we had a lot of smaller sized rocks in the mix. A quick post on the Backyard Aquaponics Forum yielded another gardener who had used a similar size media and it was successful. His only recommendation was to add composting worms to help keep the root matter cleaned up out of the beds.
With the momentary panic addressed, we started washing gravel. We used a frame made of 2x4's and 2X6's with a piece of hardware cloth that we normally use over the wheelbarrow for screening compost.
We initially added a layer of 1/4 wire mesh, however, it turned out not to be fine enough with the smaller gravel. We then added a layer of window screening that proved to be very effective at allowing water and dirt through but keeping the gravel in. We set the box over a stock tank we recently purchased and started washing, agitating the gravel with the hose nozzle.
The dirty water was diverted to our rain garden that was happy to do it's part.
It was very exciting to get to the point of adding gravel to the growbeds. I added some citrus trees, strawberries and broccoli that had been growing in the greenhouse as we went along and by the end of the day, the beds were full and we were tired but it looked beautiful.