The Border Inspection

Every coral you add to your tank arrives as an immigrant, and some of them are smuggling. Coral pests — the hitchhiking flatworms, snails, crabs, and anemones that ride in on new frags — are almost entirely preventable, and almost entirely miserable to eradicate once established. The difference between a keeper who battles pest outbreaks for years and one who never sees them is not luck. It is a border inspection: dip and quarantine every coral, without exception, before it touches the display.

This chapter is that protocol, plus a field guide to the pests you are keeping out.

The Doctrine: Nothing Enters Unchecked

The single most important sentence in this chapter: no coral goes straight from the bag into your display tank. Not from a trusted store, not from a friend, not ever. Every coral gets dipped and inspected, and ideally quarantined, first. This one habit prevents the overwhelming majority of pest disasters, because pests are far easier to stop at the border than to remove from an established reef full of rock they can hide in.

It feels excessive right up until the first time you skip it and introduce something that takes months to eradicate. Ask any experienced reefer about their worst pest story and it always begins with a coral that went straight in.

The Dip

Dipping is a short bath in a solution that irritates or kills pests while the coral tolerates it. A commercial coral dip — usually a concentrated plant-derived compound — is mixed into a container of tank water, and the coral is bathed in it for the time the instructions specify, typically five to fifteen minutes.

The technique matters as much as the solution:

1. Mix the dip into a container of your tank's water, never straight display water, at the dosage on the label.
2. Bathe the coral, and while it soaks, gently swish it and use a pipette or turkey baster to blow the solution into every crevice, under the base, and around the plug. Pests hide; the swishing dislodges them.
3. Watch what falls off. This is the inspection. Flatworms, tiny snails, crabs, and worms will drop off or become visible against the container bottom. This tells you what the coral was carrying.
4. Rinse in a separate container of clean tank water so the dip and dislodged pests do not ride along, then mount or place the coral.
5. Discard the dip water and the plug's original rubble if you can move the coral to a fresh plug, since eggs often cling to the original mount.

Critically, dips kill many mobile pests but rarely their eggs. This is why a single dip is not a guarantee, and why quarantine matters.

Quarantine

A coral quarantine is a separate, simple tank — even a small bare-bottom system with a light, a heater, and a pump — where new corals live for a few weeks before joining the display. Quarantine does what a single dip cannot: it gives pest eggs time to hatch, so you can dip again and catch the newly emerged generation, and it isolates any disease or pest you missed from your main system entirely.

A practical protocol: dip a new coral, place it in quarantine on a bare plug, observe for two to four weeks, dip again mid-way to catch hatched eggs, and only then move it to the display. It is the same logic as fish quarantine, and while many reefers skip coral quarantine and rely on dipping alone, the ones who never suffer a pest outbreak almost all quarantine. At minimum, dip everything; quarantine is the upgrade that makes you nearly bulletproof.

A Field Guide to the Enemy

Know what you are watching for.

Aiptasia. Small brown glass anemones that reproduce explosively and sting corals. They ride in on rock and coral bases. Once established they are a long war fought with targeted treatments and predators like certain filefish and peppermint shrimp. Keeping them out via dipping and inspection is vastly easier than removing them.

Coral-eating flatworms. Acropora-eating flatworms (AEFW) and zoa-eating nudibranchs are among the worst, because they are camouflaged, eat the coral directly, and their eggs survive dips. These are the pests quarantine and repeat-dipping specifically target.

Red bugs. Tiny yellow crustaceans with a red dot that infest Acropora, slowing growth and stressing the coral. Visible only on close inspection, which is exactly why you inspect.

Montipora-eating nudibranchs. White, well-camouflaged, and devastating to montipora colonies. Dip and inspect every montipora.

Vermetid snails. Sessile snails that build a hard tube on the rock and cast a mucus net that irritates nearby corals. Not deadly but annoying and hard to fully eliminate once spread.

Bristleworms and pods are generally harmless or beneficial, so do not panic at every worm — most of what falls off in a dip is harmless detritivore life. Learn to tell the destructive few from the beneficial many.

Inspection as a Habit

Dipping and quarantine are events; inspection is a habit. Get in the routine of actually looking closely at your corals — under magnification if needed — for the telltale signs: unexplained tissue loss, bite marks, a coral that will not open, tiny eggs in neat rows on the skeleton, small moving specks. Catching a pest when it is one flatworm is trivial; catching it when it is a hundred is a project. A coral that suddenly stops opening for no chemical reason should always make you check for pests, using the same tools from your coral fragging kit — a scalpel and cutters let you excise an infested section or remove eggs before they spread. This inspection habit pairs directly with the diagnostic reading covered back in the LPS chapter.

When a Pest Gets In Anyway

Even careful keepers occasionally miss something, and a pest establishes in the display. Do not panic, and do not nuke the whole tank. Identify the pest first, because the response depends entirely on what it is — an aiptasia outbreak, an AEFW infestation, and a few vermetid snails call for completely different treatments.

For many pests, targeted removal is the first line: excise an infested branch, pull the affected coral to a quarantine tank for repeated dipping, or introduce a natural predator suited to that pest. Aiptasia yield to targeted injection treatments and to predators like peppermint shrimp and certain filefish. Coral-eating flatworms require removing affected corals for a course of dips spaced to catch hatching eggs. Red bugs and montipora nudibranchs each have their own specific treatments.

The general principle is patience and specificity over brute force. Whole-tank chemical treatments are a last resort that often harm your corals and beneficial life as much as the pest. Isolate, treat the affected corals in quarantine, break the pest's life cycle with repeated dips, and let your inspection habit confirm the tank is clean before you relax. A pest caught early and treated specifically is a manageable annoyance; the disasters come from ignoring one until it is everywhere. Your dip bottle, a sharp eye, and a simple quarantine tank are a border that keeps almost everything out for years.

FAQ

How do I dip corals before adding them to my tank?

Mix a commercial coral dip into a container of your tank water at the labeled dose, bathe the new coral for the specified time, usually five to fifteen minutes, and swish it while blowing the solution into every crevice with a pipette. Watch which pests drop off, rinse the coral in separate clean water, and ideally move it to a fresh plug since eggs cling to the original mount.

Do coral dips kill pest eggs?

Usually not. Most dips kill or dislodge mobile adult pests but leave eggs intact, which is the main limitation of dipping alone. That is why quarantining new corals for a few weeks and dipping a second time matters: it lets eggs hatch so the newly emerged pests can be caught before the coral ever enters your display tank.

Do I really need to quarantine corals?

At minimum you should dip and closely inspect every coral, which stops most pests. Quarantine is the upgrade that makes you nearly bulletproof, because it isolates new corals while eggs hatch and lets you dip again to catch them. Many reefers rely on dipping alone and mostly get away with it, but those who never suffer a pest outbreak almost all quarantine new corals.