Richard bray

Rockwool
Rockwool was originally used as insulation, but has become the primary growing media in hydroponics and aquaponics. Basalt is melted down into a liquid, and spun like cotton candy into a fibrous block. The block is then formed into cubes, and holes are pressed into the top for seeds.
Rockwool blocks are incredibly porous, which helps them trap nutrients as water flows through. Seeds can be directly planted into blocks, and then transplanted into netted pots.
Soak cubes in a tub before planting seeds and wait until all the air bubbles have escaped, which signals that the block is thoroughly saturated. Allow the blocks to drain, but do not wring out excess water. Plant seeds into the blocks, and keep them in a seed-starting tray with a humidity dome until germination.
The major disadvantage of using rockwool is the cost per cube, considering they are not reusable.
Growing Media
Growing media can be used to support a rockwool cube inside a netted pot, or as a replacement for rockwool inside a netted pot. Heavier grow media offers more stability, which is why clay pebbles and river rock are the most popular media choices for deep-channel production.
If you decide not to use rockwool, you will need to germinate seeds in a seed-starting plug or sponge. Seeds planted directly into growing media will wash through, so they need extra support until the root system can spread out.
Hydroponic supply companies sell many seed-starting plugs, but many are made from organic materials. These materials can affect pH and nutrients, and can clog the system as they break down. Synthetic plugs and sponges can give seedlings support until they grow through the media. For small systems, you can cut your own plugs from cheap household sponges.
Grow Beds
DWC grow beds are similar to media-filled beds, except they aren’t filled with media. Most DWC systems use a continuous-flow circulation method, so water is constantly circulating through the system.
Grow beds for DWC systems can be shallower than media-filled beds, but this will also limit plant selection. DWC systems are best for leafy greens, herbs, and small fruiting vegetables, because they have smaller root systems and require less nutrition.