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hobbyists and in developing regions. However, it is uncommon to find commercial production using only media beds as they are less productive than other types discussed below. Rule of Thumb for media systems are detailed in Table 1.
Table 1: Rules of thumb for media-based aquaponic systems.
| Rules of Thumb for Media-Based Aquaponic Systems |
| Substrate Characteristics | • Porous to increase oxygen and water retention
• Provide adequate drainage
• Easy to handle
• Light-weight
• Cost effective |
|---|
| System Design | • Plant beds should be at least 12 inches (30 cm) deep
• Water should remain 2 inches below the surface of the media to prevent algae from growing in the surface of the media
• Media displaces 60% of the volume of the plant bed. Fish tanks or sumps should be sized so the pump does not run dry and tank does not overflow during the flood and drain cycle.
• 1:1 ratio of fish tank volume to plant bed volume for simple design involving solely a fish tank and plant bed.
• 2:1 or 3:1 ratio can be achieved by addition of the sump (Figure 5) |
|---|
| Carrying Capacity | • Low fish stocking density
• Separate solids filtration needed for increase fish density
• Feeding rate is 25-40% less than values reported for deep water culture |
|---|
| Water Flow Management | • Fish tank volume should be circulated through the plant bed every hour
• Water flow |
|---|
| Maintenance | • Cleaning required at regular intervals to remove solids
• Red worms can be added to move solids trapped in beds |
|---|
A variety of materials can be used as substrate, including pea gravel, lava rock, expanded clay pebbles, or other inert media; practitioners may be limited by what is locally available. Water flow in the system is controlled by either a timer or siphon. Using the timer method, water is pumped for a set amount of time, allowing the bed to fill. When the timer shuts off, water drains until the timer engages the pump again. The siphon method is often implemented using an
FIGURE 7a, 7b
Bell siphon (a) or loop siphon (b)
automatic bell siphon (Figure 7a) or loop siphon (Figure 7b). In both siphon methods, the pump runs continuously, controlling how fast the bed fills and drains. Fox et al. (2010) gives comprehensive, step-by-step instructions for building, operating, and troubleshooting an automatic bell siphon.