How to Acclimate New Coral: Float, Drip, and Dip
Coral shipped across the country arrives cold, oxygen-depleted, and swimming in ammonia. How you handle the first two hours determines whether it thrives or crashes. Here is the full process.
Coral shipped for 24 to 48 hours arrives in a stressed state. The water in the bag has cooled significantly, oxygen has been depleted, and ammonia has accumulated from the coral's waste with nowhere to go. Salinity may have drifted. Dumping a coral from that environment directly into your display tank — even one with perfect parameters — creates a sudden shock across temperature, salinity, and chemistry. That shock alone can trigger bleaching or kick off a tissue recession that kills the animal within days.
Acclimation closes the gap between the bag environment and your tank environment slowly enough that the coral can adjust without triggering a stress response. The full process takes about an hour and has four steps.
Step 1 — Float the Bag
Place the sealed shipping bag directly into your sump or display tank and let it float for 15 to 20 minutes. Do not open it yet. This step equalises temperature only — the bag water gradually warms (or cools) to match your tank. It does nothing for salinity, pH, or chemistry, which is why you still need to drip acclimate afterward.
If you have multiple bags, float them all simultaneously. Do not leave bags floating for more than 30 minutes before moving to the next step — CO2 buildup in the sealed bag continues and pH will drop further.
Step 2 — Drip Acclimate
Open the bag and pour the coral and all its water into a clean container — a small bucket or a dedicated acclimation container works well. The goal now is to gradually replace the bag water with your tank water, allowing the coral to adjust to your parameters over 30 to 45 minutes.
Use a length of standard aquarium airline tubing tied in a loose knot near one end. Place the other end in your display tank or sump and start a siphon by sucking briefly. Tighten or loosen the knot until you achieve a drip rate of about 3 to 4 drops per second. Let the container fill until the water volume has approximately doubled.
When complete, discard the container water. Do not pour it into your display tank — it contains the accumulated ammonia from shipping and may carry hitchhiker pests.
Step 3 — Coral Dip
Always dip new coral before it enters your tank. Every piece of coral — even from a trusted source — can carry pests that are invisible to the naked eye. A single coral with Acropora-eating flatworms or zoanthid-eating spiders can seed an infestation that takes months to eradicate.
Mix your dip solution in a separate container using tank water (not the bag water). Follow the product's concentration and timing instructions precisely.
Coral Dip Options
- CoralRx: The most widely used broad-spectrum dip. Effective against a wide range of flatworms, nudibranchs, copepods, and other external parasites. The standard dip time is 10 to 15 minutes with gentle agitation. Works well on most coral types including SPS, LPS, and softies.
- Revive: A gentler formulation better tolerated by sensitive softies, zoanthids, and mushrooms. Good choice for coral you are concerned about stressing further, at the cost of being slightly less effective against some pests.
- Bayer insecticide (diluted): Effective and cheap — the active ingredient (imidacloprid) is lethal to most arthropod pests including AEFW. Controversial because it is an off-label use of a pesticide not formulated for aquarium use. Many experienced reefers use it routinely with no observed coral harm at correct dilutions. Research the current recommended dilution ratio before use and do not use on LPS or sensitive softies.
- Iodine dip: Lugol's iodine diluted in tank water. A mild dip suitable for softies and zoanthids. Effective as a general antibacterial and against some surface-level hitchhikers, but not as effective against flatworms as CoralRx or Bayer. Good as a second dip after a primary treatment.
What to Look For During the Dip
Agitate the container gently and inspect the dip water and the coral surface. Common hitchhikers that dislodge during a dip:
- Red planaria (flatworms): Flat, rust-red or brown worms about 3–5 mm long. Common on soft corals, zoanthids, and some LPS. They cover coral tissue and block light, starving it slowly.
- Acropora-eating flatworms (AEFW): Tiny (1–2 mm), pale, nearly transparent flatworms that hide on the underside of Acropora branches. Look for white bite marks on the coral surface. One of the most damaging pests in an SPS tank.
- Zoanthid-eating spiders: Small crustaceans that hide among zoanthid polyps and eat them from within the colony. Easily missed during visual inspection; dipping forces them out.
- Montipora-eating nudibranchs: Tiny white nudibranchs that feed exclusively on montipora. Hard to see against the coral surface; dipping causes them to detach and become visible.
- Tissue that is receding or disintegrating: Rapid tissue necrosis (RTN) can be triggered by shipping stress. If you see tissue pulling back rapidly from the skeleton during the dip, the coral may have RTN — frag any healthy tissue immediately and dip the frags separately.
Step 4 — Placement
New coral should not go directly to its intended final position. Even if you know a coral is high-light and high-flow, it arrived from an environment with different light intensity, spectrum, and flow rate. Placing it immediately at full intensity stresses it further.
Start new coral lower in the tank and in lower flow than its target position. Over 2 to 4 weeks, move it gradually upward and into higher flow as it extends fully and shows healthy polyp behavior. This gradual introduction reduces bleaching from light shock and flow stress.
Do not place new coral touching or near existing coral. Chemical allelopathy is real — corals release compounds that inhibit neighboring competitors, and a stressed new coral next to an established colony may decline faster than it would in isolation.
Normal Settling vs. Stress Signals
- Normal: Sliming (mucus film over the coral surface) — a common stress response that resolves within hours to a day.
- Normal: Closed or retracted polyps for 1 to 3 days after placement. Most coral needs time to assess the new environment.
- Concern: Polyps still closed after 5 or more days. Check parameters, flow, and allelopathy from neighboring coral.
- Problem: Tissue recession progressing from the base or edges. Move the coral to a recovery area and address water quality.
- Serious: Rapid bleaching (coral turning white) within 24 hours. This is usually light shock — move to lower light immediately.
