Determining the Ideal Amount of Live Rock for a Coral Tank

 

Live rock serves as both biological filtration and habitat foundation in reef aquariums. The general rule is to use 1-1.5 pounds of live rock per gallon (or 0.5-0.7 kg per liter) of tank volume. For example:

 

  • A 50-gallon tank: 50-75 pounds (22-34 kg)
  • A 100-gallon tank: 100-150 pounds (45-68 kg)

 

Key Considerations

  1. Biological Load
    • Live rock hosts nitrifying bacteria that process waste. Understocking risks ammonia spikes, while overstocking may reduce swimming space for fish.
  2. Aesthetic vs. Functional Balance
    • Branchy rocks (e.g., Fiji rock) provide more surface area for coral attachment but require careful stacking to avoid instability.
    • Dense rocks (e.g., base rock) are ideal for structural support but may limit coral placement options.
  3. Coral Compatibility
    • Soft corals (e.g., mushrooms) thrive on moderate rock coverage (~30% of tank floor), while SPS corals (e.g., Acropora) need open water flow and sparse rock clusters.

 

Step-by-Step Placement Guide

  1. Start with a base layer of larger, flat rocks to distribute weight evenly.
  2. Build vertical structures using porous rocks to maximize surface area.
  3. Leave 30-40% of the tank floor open to prevent detritus buildup.

 

Pro Tip: Always leave gaps between rocks to ensure water circulation and prevent dead zones.

For nano tanks (<30 gallons), use smaller, lightweight rocks to avoid excessive weight. Always quarantine new live rock to prevent pest introductions.