The Five Pests You Will Actually Meet

Almost every pest in a reef tank arrives on a frag plug. Dip everything, quarantine what you can, and learn to recognize these five, because the difference between a nuisance and a wipeout is how early you catch it.

1. Aiptasia

Looks like: a small brown anemone with a long stalk and clear tentacles, tucked in a crevice, multiplying every week.
Damage: stings corals near it and takes over rock.
Fix: peppermint shrimp (the true Lysmata wurdemanni) for a light infestation, a Berghia nudibranch for a heavy one, or an aiptasia specific injection kit for a few large ones. Never cut or scrape it: every fragment becomes a new animal.

2. Montipora eating nudibranchs

Looks like: a tiny white or cream slug, three to five millimeters, perfectly camouflaged on the coral. You usually notice the damage first: a receding line of white skeleton advancing across a plate.
Damage: fatal to montipora, and only montipora.
Fix: remove the colony, blow it out with a baster, dip it, and inspect the plug with a flashlight for the small clusters of eggs. Repeat every five days for three weeks, because dips kill adults and not eggs.

3. Acropora eating flatworms

Looks like: a flat, transparent worm shaped exactly like the coral tissue it sits on. The reliable tell is the bite marks and the small dark egg saddles along the base of the branches.
Damage: pale patches, no polyp extension, slow decline of an acro that has no other reason to be unhappy.
Fix: dip the coral in a coral specific dip, blow the branch hard while it is in the dip, and inspect the base. Same three week schedule for the eggs. A six line wrasse helps but it is not a cure.

4. Red bugs

Looks like: yellow dots with a red spot, half a millimeter, only on smooth skinned acropora. Easiest to see on a white or pale branch under a flashlight.
Damage: polyps stay closed and growth stops, but the coral rarely dies outright.
Fix: treatment is a whole tank decision and it affects your shrimp and crabs, so read carefully before dosing anything. Quarantine and dipping are the sane path for a single frag.

5. Zoa eating spiders and nudibranchs

Looks like: a small spider like animal, or a nudibranch colored exactly like the zoa it is eating. Both hide at the base of the polyps by day.
Damage: polyps stay closed, then disappear one by one from the edge of the colony.
Fix: take the rock out, dip it, and scrub the base with a soft toothbrush in tank water. Check the plug seam, which is where they hide, and repeat weekly for a month.

The routine that prevents all five

1. Dip every single new coral, including ones from a friend and ones from us.
2. Discard the plug when you can, and glue the frag onto your own rock or a fresh plug.
3. Quarantine for two to four weeks if you have the space.
4. Once a week, after lights out, walk the tank with a flashlight. Almost everything on this page is only visible then.