Grow Media for Aquaponics

Plants need something to grab onto with their roots for physical support. The ideal media is pH neutral, light weight, and cheap with no sharp edges, doesn't break down, and is easy to clean.

Size: If your grow media is too small, it'll get clogged up with solid waste and will prevent a good circulation of air and water for your plant's root zones. Grow media that's too big won't allow plant roots to properly establish themselves due to the large air pockets created from big media. Ideally, you want your aquaponics grow media to be approximately 12-18mm in diameter. About 1/2 inch.

• Expanded Clay (Hydroton): Probably the best, except for the expense. Extremely light, pH neutral, easy to clean and sterile.
• Expanded Shale: Excellent! pH neutral and has more rounded edges which makes it easy on the hands and plant roots.
• Gravel: Heavy, and must be pre-cleaned. Can cause pH problems. Watch out for sharp edges. Very low cost.
• River rock: Heavy, can cause pH issues, but not sharp and usually doesn't require pre-cleaning.
• Coconut chips: similar to clay pellets in terms of water holding capacity and their porous structure enables roots to easily penetrate through.

Keeping the media moist but not wet is important for some types of plants; those which can get "root-rot" if they are too wet. This can be done by several methods:
 

• Flood and Drain. The bed and media are first flooded with water, then drained and allowed to dry. There are a couple of ways to do this:
  • Just turning a pump on and off. Generally a great way to do it, but it does require a system design where the pump can be turned off. E.g. if you depend on the pumped water for oxygenation, you would need a second pump. And you need a way to turn on and off the pump; a pump controller. Of course, that means you can exactly control the on and off times.
  • Bell Siphons. This is the most common but can be difficult to get working reliably. Probably the best design is Affnans^: (click for a bigger view)
    
• Wicking. A cloth or other mesh is placed between the media and the water. Moisture wicks up from the water and spread out into the media.
• Drip. Although it seems like an obvious solution, drip irrigation from water that has fish in it generally fails due to solids in the water which clog the emitter or filter. A good, and easily cleaned filter stage can help avoid this issue.