For a reef tank utilizing the Berliner method, the quantity of rock needed is generally 10 to 20% of the water volume.
The Role of Live Rock in a Reef Tank
In the context of a reef aquarium, particularly when following the popular Berliner method, live rock serves a crucial function: biological filtration. These porous rocks are teeming with beneficial bacteria and micro-organisms that break down harmful waste products like ammonia and nitrite, maintaining water quality essential for marine life. The quantity of rock is therefore directly related to the volume of water it needs to filter.
Recommended Quantity
Based on the Berliner method, the recommended amount of live rock is proportional to the aquarium's water volume. Generally, aquarists use an amount of rock equivalent to 10 to 20 percent of the total water volume. This range provides sufficient surface area for the necessary biological filtration.
Factors Influencing Quantity
While the 10-20% rule is a common guideline, the exact amount within this range depends on several factors:
- Quality and Density of the Rocks: Not all live rock is created equal. Highly porous and "light" rock provides more surface area for bacteria per pound or volume compared to dense, heavier rock. Better quality, more porous rock means you might need less (closer to the 10% end), while denser rock might require more (closer to the 20% end).
- Aquarium Stocking Level: Tanks with a higher bioload (more fish or corals producing waste) may benefit from more live rock to handle the increased demand on biological filtration.
- Aesthetic Preference: Beyond filtration, live rock is also used to build aquascapes, providing structure and hiding places for inhabitants. Your desired look will influence the total amount used, potentially pushing towards the higher end of the range or even slightly beyond, provided it doesn't compromise water flow.
Calculating Rock Volume
To determine the amount of rock you need, calculate 10% and 20% of your tank's water volume. Remember that rock is often sold by weight, but the volume and porosity are what matter most for filtration. Lighter, more porous rock offers more filtration per pound.
Here's a simple table showing the estimated rock volume needed for common tank sizes:
| Tank Size (US Gallons) | Water Volume (Liters) | 10% Rock Volume (Gallons) | 20% Rock Volume (Gallons) |
|---|---|---|---|
| 20 | ~75.7 | ~2.0 | ~4.0 |
| 40 | ~151.4 | ~4.0 | ~8.0 |
| 75 | ~283.9 | ~7.5 | ~15.0 |
| 100 | ~378.5 | ~10.0 | ~20.0 |
| 150 | ~567.8 | ~15.0 | ~30.0 |
Note: These figures represent the volume the rock displaces. The weight can vary significantly based on the rock's density.
When purchasing rock, consider its porosity. High-quality, lightweight, porous rock is often preferred for its superior surface area for biological filtration.
