Coral Frags for Beginners: What to Know Before You Buy

Q: What exactly is a 'coral frag,' and why are corals sold this way?

A frag (short for 'fragment') is a small piece of a larger coral colony that's been cut, broken, or naturally separated and then mounted on its own — typically on a small ceramic or rock 'frag plug' — so it can grow into an independent colony over time. This works because, as covered in our overview of what coral actually is, most corals kept in the hobby are colonial animals: a colony is made up of many genetically identical polyps, and a piece containing even a small number of polyps can, under the right conditions, grow into a full colony of its own. Selling and trading frags is the dominant way corals move through the hobby — it lets keepers propagate corals they already have (see our guide on fragging hammer corals for what this looks like for one common LPS genus) and lets buyers start with a smaller, often less expensive piece than a full colony.

Q: Do I need to dip a new coral frag before adding it to my tank?

Dipping is widely recommended as a preventive step, even for frags that look clean — our coral dip and aiptasia guide covers this in detail, but the short version is that a brief dip in a coral-safe treatment solution can kill or dislodge small hitchhikers (aiptasia, flatworms, pest snail eggs, and some bristle worms) that can be easy to miss with a visual inspection alone. After dipping, rinse and inspect the frag again before adding it to your tank — dipping isn't a substitute for the inspection, it's an additional layer on top of it. This step matters more than it might seem: a single missed aiptasia or flatworm on one frag is a common way these pests get established in an otherwise clean tank.

Q: How do I mount and place a new frag, and how should I expect it to look at first?

Most frags are attached to rock using cyanoacrylate (super) glue — our reef-safe super glue guide covers what to look for — or sometimes a two-part epoxy putty, both of which cure quickly underwater and are considered safe for reef tanks when reef-specific products are used. For placement, it's worth thinking ahead to the coral's likely eventual size and, for species like hammer or torch corals that extend sweeper tentacles, its future reach — not just how much room the small frag currently takes up. As for appearance: it's common for a new frag to look less extended, duller, or 'closed up' for some period after placement, especially if it's been shipped or moved between different lighting and flow conditions. This is often a normal acclimation response rather than a sign of a problem, though it's still worth keeping an eye on the frag over the following days and weeks to confirm it's settling in rather than declining.

By Hektor Jorgo Published May 28, 2024 Updated June 14, 2026 5 min read

A small coral frag mounted on a frag plug, recently placed in a reef aquarium

Quick Facts

What a Frag Is: A small piece of a larger coral colony, cut or broken off and mounted separately so it can grow into its own colony
Why Frags Exist: Because corals are colonial animals, fragments of a colony can each grow independently — the basis of most coral propagation in the hobby
Before Buying: Inspect for visible pests, tissue recession, or unusual coloration/discoloration on the frag and its base rock
Dipping: A coral dip before adding a new frag to your tank helps address hitchhiking pests like aiptasia, flatworms, and pest snail eggs
Mounting: Frags are commonly attached to rock with cyanoacrylate (super) glue or epoxy putty
Acclimation: New frags often benefit from lower, more indirect placement initially, especially if shipped or moved between different lighting conditions
Initial Appearance: Frags often look less extended or 'closed up' for a period after placement — this is commonly a normal adjustment response, not necessarily a problem
Placement Planning: Consider the coral's eventual size and any sweeper tentacle reach, not just its current size as a small frag

Buying your first coral frag is a small purchase that comes with a surprising number of questions — what to check before handing over money, what to do with it the moment you get home, and how worried to be if it doesn't look amazing on day one.

Short Answer

A coral frag is a small piece of a larger coral colony, mounted on its own so it can grow into an independent colony — a direct consequence of corals being colonial animals where fragments can each grow on their own. Before buying, a quick visual check for pests, recession, or unusual discoloration is worth doing. After buying, dipping (covered in detail in our coral dip guide) and a careful rinse-and-inspect step help prevent hitchhikers from reaching your tank, and mounting with reef-safe glue followed by placement that accounts for the coral's future size gives the frag its best start. A new frag looking less extended or "closed up" for a while after placement is common and often just acclimation.

What a Frag Actually Is

As covered in our overview of what coral is, most corals kept in reef tanks are colonial — a coral "individual" is really a group of genetically identical polyps connected to and supporting each other. A frag (fragment) is a piece cut, broken, or naturally separated from a larger colony and mounted on its own, typically on a small ceramic, resin, or rock frag plug. Given the right conditions, that piece can grow into a full colony in its own right.

This is the basis of most coral propagation in the hobby — keepers fragment corals they already have (our hammer coral fragging guide shows what this process looks like for one common LPS genus) both to manage colony size and to create new frags to trade or sell, and buyers get a smaller, often less expensive starting point than a full colony.

Before You Buy: What's Worth Checking

A quick visual inspection — in person if possible, or via clear photos/video for online purchases — can save some headaches later:

Pests and hitchhikers — look at the frag itself and its base rock for anything that doesn't belong: small anemones, worms, or anything moving unexpectedly
Tissue recession — areas of bare skeleton on an otherwise living coral, similar to what's discussed in our brain coral skeleton guide, can indicate an existing health issue (though a small, stable area of recession isn't necessarily disqualifying)
Discoloration — pale, bleached-looking tissue can indicate stress or zooxanthellae loss, the kind of process covered for anemones in our bleaching guide, which applies to corals as well

None of these are automatic dealbreakers on their own, but they're useful context for both the purchase decision and for what to expect from the frag in its first weeks in your tank.

Dipping and Inspecting: The Step That's Easy to Skip

Even a frag that looks completely clean can carry hitchhikers too small to easily spot — aiptasia, flatworms, or pest snail eggs are common examples. Our coral dip and aiptasia guide covers this in detail, but the short version for a new frag is:

Dip the frag in a coral-safe treatment solution, following the product's instructions
Rinse it afterward
Inspect again, looking specifically for anything dislodged by the dip

This sequence matters because dipping and inspecting are complementary, not redundant — a dip can dislodge something an inspection alone would miss, but the post-dip inspection is what actually catches it before it ends up in your tank.

Mounting and Placement

Frags are typically attached to rock with:

Cyanoacrylate (super) glue — fast-curing, widely used, and covered in more detail (including reef-safety considerations) in our super glue guide
Two-part epoxy putty — also commonly used, particularly for larger or more awkwardly shaped pieces

For placement, it helps to think beyond the frag's current size:

Eventual colony size — a small frag can grow considerably; leaving room for that growth avoids needing to relocate it later
Sweeper tentacle reach — for species like hammer and torch corals, the coral's reach at night can extend well beyond its daytime footprint and affect neighboring corals

What to Expect in the First Days and Weeks

It's common for a newly placed frag to look less extended, duller in color, or generally "closed up" for a period after placement — especially if it's been shipped or moved between tanks with different lighting and flow. This is often a normal acclimation response rather than a sign of trouble. That said, it's still worth monitoring the frag over the following days and weeks to confirm it's gradually extending and settling in, rather than continuing to decline — the same general "watch for the trend, not just one observation" approach covered in our guide on reading coral recession.

Quick Reference

A frag is a small piece of a larger coral colony, mounted separately to grow into its own colony
Before buying, check for visible pests, tissue recession, and unusual discoloration
Dip new frags before adding them to your tank, then rinse and inspect again afterward
Mount frags with reef-safe cyanoacrylate glue or epoxy putty
Plan placement around the coral's eventual size and any sweeper tentacle reach
A new frag looking "closed up" for a while after placement is often normal acclimation
Monitor over days and weeks for the trend (improving vs. declining), not just one look

Frequently Asked Questions

What exactly is a 'coral frag,' and why are corals sold this way?

A frag (short for 'fragment') is a small piece of a larger coral colony that's been cut, broken, or naturally separated and then mounted on its own — typically on a small ceramic or rock 'frag plug' — so it can grow into an independent colony over time. This works because, as covered in our overview of what coral actually is, most corals kept in the hobby are colonial animals: a colony is made up of many genetically identical polyps, and a piece containing even a small number of polyps can, under the right conditions, grow into a full colony of its own. Selling and trading frags is the dominant way corals move through the hobby — it lets keepers propagate corals they already have (see our guide on fragging hammer corals for what this looks like for one common LPS genus) and lets buyers start with a smaller, often less expensive piece than a full colony.

What should I check before buying a coral frag?

A few things are worth a close look, ideally in person or via clear photos/video if buying online: visible pests or hitchhikers on the frag itself or its base rock (small anemones, worms, or anything moving that doesn't belong), areas of tissue recession or bare skeleton (similar to the recession discussed in our brain coral skeleton guide) that might indicate an existing health issue, and unusual discoloration — pale or bleached-looking tissue can indicate stress (the kind of zooxanthellae loss covered in our anemone bleaching guide, which applies to corals too). None of these automatically mean 'don't buy it' — a frag with a small area of stable recession, for example, may otherwise be healthy — but they're worth factoring into the decision and into your expectations for how the frag will look in its first weeks in your tank.

Do I need to dip a new coral frag before adding it to my tank?

Dipping is widely recommended as a preventive step, even for frags that look clean — our coral dip and aiptasia guide covers this in detail, but the short version is that a brief dip in a coral-safe treatment solution can kill or dislodge small hitchhikers (aiptasia, flatworms, pest snail eggs, and some bristle worms) that can be easy to miss with a visual inspection alone. After dipping, rinse and inspect the frag again before adding it to your tank — dipping isn't a substitute for the inspection, it's an additional layer on top of it. This step matters more than it might seem: a single missed aiptasia or flatworm on one frag is a common way these pests get established in an otherwise clean tank.

How do I mount and place a new frag, and how should I expect it to look at first?

Most frags are attached to rock using cyanoacrylate (super) glue — our reef-safe super glue guide covers what to look for — or sometimes a two-part epoxy putty, both of which cure quickly underwater and are considered safe for reef tanks when reef-specific products are used. For placement, it's worth thinking ahead to the coral's likely eventual size and, for species like hammer or torch corals that extend sweeper tentacles, its future reach — not just how much room the small frag currently takes up. As for appearance: it's common for a new frag to look less extended, duller, or 'closed up' for some period after placement, especially if it's been shipped or moved between different lighting and flow conditions. This is often a normal acclimation response rather than a sign of a problem, though it's still worth keeping an eye on the frag over the following days and weeks to confirm it's settling in rather than declining.

Sources & Further Reading

About the Author: Hektor Jorgo

Co-Founder & Marine Biologist

Hektor is a co-founder of Sea Life Planet and has kept reef and freshwater aquariums for over 15 years. He holds a background in marine biology and focuses on species care accuracy, water chemistry, and tank husbandry.