Why is sand preferred over other media like gravel in iAVs?

This is covered in Chapter 20 in the iAVs Handbook

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Sand is the ideal medium for iAVs due to its superior filtration properties, enhanced oxygenation, and ability to promote a thriving microbial community. Unlike gravel or expanded clay pebbles, which have limited surface area and can lead to anaerobic zones, sand:

• Traps solid waste near the surface, facilitating breakdown and preventing clogging.
• Promotes oxygen exposure throughout the bed, accelerating decomposition and supporting aerobic microbes crucial for nitrification.
• Provides a vast surface area for beneficial bacteria to colonize, maximizing nutrient cycling efficiency.
• Retains moisture while allowing excess water to drain, creating an ideal balance for plant growth.