Clownfish on anemone

Week 12. All Saltwater Aquarium Rocks!

Updated 2023

In this week’s session, we’ll dive deep into the realm of reef rocks—an unexpectedly complex subject in the world of saltwater aquariums. Over the past two decades, this hobby has undergone significant changes, resulting in a plethora of terms that can be confusing or even contradictory. While the notion of rocks might seem unassuming, you’re likely beginning to realize the crucial role that the right type, size, and quantity of reef rocks play in the success of your saltwater aquarium.

This Week's Video:

Basics of Reef Rock

Unveiling the Essence of Reef Rock

The term “Reef Rock” carries profound significance, underlining the fact that not all rocks are suitable for a saltwater aquarium. In fact, it’s strongly advised against using just any random rock. This caution is warranted due to the potential presence of contaminants and the unique benefits that authentic reef rock offers—benefits that other rocks cannot replicate.

Reef rocks are primarily composed of aragonite, a type of calcium carbonate. They are either naturally sourced from quarries, oceans, or crafted through human intervention. Being essentially ancient coral skeletons, they exhibit chemical compatibility with saltwater environments and boast high porosity. This porosity offers an ample habitat for beneficial filtering bacteria and other microorganisms. Ensuring space for these vital inhabitants is pivotal for the well-being of your aquarium, with reef rocks being an optimal solution.

Terminology Decoded

Let’s clarify the terms that might cause confusion. Rocks can be classified as wet or dry. Wet rocks are often referred to as “live rock” due to their colonization by bacteria and organisms, expediting aquarium maturation. Conversely, dry rocks can be either artificially produced or extracted from quarries, having never been in an ocean or aquarium environment. The majority of rocks available for purchase fall under the category of dry rocks.

In the past, “dry-live rock” was prevalent—formerly live rock that was dried out. These rocks, however, retained significant organic matter that could lead to future problems. It’s advisable to avoid this type of rock unless you’re prepared to take extra precautions to ensure safety. When in doubt about the rock’s terminology or origin, refer to the product description for clarifications.

Origins of Reef Rock

As previously mentioned, reef rocks can be sourced through artificial means, quarries, or direct extraction from oceans. Previously, ocean-sourced live rock wasn’t sustainable, as it involved destructive practices damaging existing reefs. However, the landscape has shifted, and current live rock is either matured dry rock from aquariums or placed in the ocean for a few months before harvesting.

Multifaceted Functions

The paramount role of reef rock is to provide a habitat for essential bacteria that contribute to water filtration. While reducing the amount of rock for aesthetic reasons is possible, alternative solutions like media blocks need to be employed. Furthermore, reef rock offers shelter for various critters, from copepods to small worms and crabs. This biodiversity is integral for the long-term health of your aquarium.

Additionally, fish and invertebrates require spaces for hiding, resting, and coexisting. Without proper rock structures, issues like bullying and stress can emerge, and corals lack suitable placement. Ultimately, reef rocks contribute to the aesthetic charm of your aquarium, transforming it into a slice of captivating natural beauty.

Helping You Choose your Reef Rock!

Weighing the Pros and Cons of Wet “Live” Reef Rock


The standout advantage of wet reef rocks lies in the wealth of potential bacteria, critters, and microorganisms they bring. This infusion can almost instantly mature your aquarium, boasting more biodiversity than even many established aquariums equipped with sterile dry reef rocks. While this might seem like a single benefit, its impact on your saltwater aquarium’s health and vibrancy cannot be underestimated.


Several downsides accompany wet reef rock usage, with the primary concern being the potential for unwelcome hitchhikers. Although the rock offers diverse biodiversity, not every inhabitant will be beneficial. While not a major issue, it implies preparedness to manage pests and a need to proceed cautiously before introducing desired corals and fish. Additionally, working with live rock can limit your aquascape creativity. The less predictable shapes and the need to keep the rock submerged to preserve its vitality can hinder intricate scaping. Lastly, wet reef rock is pricier than dry rock, making it less suitable for those on a budget.

Exploring the Pros and Cons of Dry Reef Rock


For many, the most significant advantage of dry reef rock is the absence of pests and other potential nuisances. While it lacks the immediate biodiversity of wet rock, it spares you from grappling with various potential issues. The dry nature of the rock also provides ample time and room for creative aquascaping. With the aid of tools, cement, or epoxy, you can fashion stunning, intricate scapes. Furthermore, dry rock is more cost-effective, allowing you to acquire substantial quantities without straining your budget.


The primary drawback of dry reef rock is its lack of inherent biodiversity. It takes time, typically a few months, for the rock to mature, and even then, it won’t match the vitality of wet live rock sourced from the ocean.

Exploring Rock Shapes

A diverse array of reef rock shapes exists, particularly within the domain of dry rocks. Recently, some companies have ventured into crafting rocks with specialized shapes to simplify the aquascaping process.

Examples include:

  • Base Rocks with flat bottoms for convenient placement.
  • Shelf Rocks with flatter tops, maximizing coral placement areas.
  • Branching rocks for intricate aesthetics and enhanced coral placement.
  • Pre-shaped rocks like arches or ones with holes, expediting captivating scaping.
  • Reef rock rubble, comprising small rock fragments useful for various purposes.
  • Reef rock “trees,” assemblies of rocks interconnected by rods to create vertical structures.

Guidance for Rock Purchase

Procuring reef rock is a straightforward endeavor. MarineDepot offers an extensive array of options. You can explore wet reef rock options online, ensuring you choose from reliable sources. Visiting your local fish store is also beneficial, allowing you to inspect the rocks in person before making a decision.

Innovation in rock designs includes a spectrum of sizes, shapes, and even colors like purple-pink. The “1 pound per 1 gallon” guideline aids in determining the required quantity, yet obtaining more than necessary can simplify the aquascaping process.

Lastly, invest in reef-safe epoxy or cement to achieve a stable and visually appealing aquascape.

Curing “Dry-Live Rock”

Should you acquire dry rock that was previously alive, such as from other hobbyists, a special process is recommended. Quarantine the rock in a container like a Brute trash can, utilizing a wavemaker and heater in saltwater. It’s crucial to shield the rock from light to enable the disposal of dead material through a natural “processing” period.

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