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How to Acclimate New Corals Safely
Acclimate a new coral in three stages: float the sealed bag 15–20 minutes to match temperature, then drip acclimate over 30–60 minutes to match salinity and pH, then dip before it touches your display water. Place the coral low and in shaded flow for the first week, then raise light and flow gradually over 2–4 weeks. The corals that fail are almost always the ones rushed straight from bag to rockwork — slow and observed beats fast and hopeful.
A new coral is at its most vulnerable in the first hour after it arrives, not the first week. It has spent hours or days sealed in a bag, breathing down its own oxygen and building up waste, and it is about to be dropped into water that is almost certainly a little different from what it just left. Acclimation is not a ritual — it is the process of closing that gap slowly enough that the coral's tissue never has to absorb a sudden shock. Get it right and most healthy corals shrug the move off within days. Rush it and you can lose a colony that survived shipping just fine.
Stage one: temperature
Temperature is the fastest-moving variable and the easiest one to get wrong by accident. Float the sealed, unopened bag in your display or sump for 15–20 minutes so the water inside gradually rises or falls to match the tank. Keep the bag sealed during this stage — the goal is only to equalise temperature, not to start mixing water yet. Avoid opening the bag under strong light; corals that have travelled in the dark can be sensitive to a sudden bright exposure on top of everything else that is changing.
Stage two: drip acclimation
Once temperature is matched, pour the coral and its bag water into a clean container and begin drip acclimation. A length of airline tubing with a valve, or a commercial drip kit, lets tank water trickle in slowly so salinity, pH and alkalinity shift gradually rather than all at once. Aim for a slow, steady drip that roughly doubles the volume in the container over 30–60 minutes — long enough for a smooth transition, short enough that the coral is not sitting in an increasingly stagnant, oxygen-poor container for hours.
| Stage | Purpose | Typical time |
|---|---|---|
| Float (sealed bag) | Match temperature | 15–20 minutes |
| Drip acclimation | Match salinity, pH and alkalinity | 30–60 minutes |
| Dip | Remove hitchhiking pests before the coral enters the display | Per product instructions, usually 5–15 minutes |
Dipping: why and how
A coral dip is a short bath in a solution designed to make hitchhiking pests — flatworms, nudibranchs, red bugs and similar — release their grip so you can rinse them away before the coral goes anywhere near your display. It is cheap insurance against a pest problem that can otherwise take months to notice and years to fully clear. Dip after drip acclimation, following the product's instructions for concentration and time, then give the coral a brief rinse in clean, temperature-matched saltwater before placement. Softer, more delicate corals sometimes react to dipping with extra polyp retraction or slime production for a day or two — that is a normal stress response, not a sign the dip failed.
Placement and the light ramp
Where a coral lands on day one matters almost as much as how it got there. Place new arrivals lower in the tank and in moderate, indirect flow for the first several days, even if the species will eventually want to sit high under intense light. A coral that has been in a dim shipping bag for days has no photo-adapted tissue built up yet, and full display lighting on day one is a common, avoidable cause of tissue bleaching that gets blamed on water quality instead.
From that low, shaded starting point, raise the coral toward its target position gradually over 2–4 weeks, watching how it responds at each step rather than following a fixed schedule. Full polyp extension, steady or improving colour, and no fresh recession are the signals that it is ready for the next move up. Retracted polyps, paling tissue or visible stress at a given light level mean pause, or drop back a step, before pushing further.
What to watch and log afterwards
The first two to three weeks after acclimation are when a coral tells you the most, and it is also the window most hobbyists forget to pay close attention to once the initial excitement fades. Note the date you first see polyps extending normally — often the clearest sign that a coral has settled in — along with any colour shift, unusual mucus, or aggression from neighbouring corals as it is worked into the aquascape. A coral that never fully opens after a week, or one that opens well and then closes again for no obvious reason, is worth investigating against your parameter log rather than assumed to be settling in on its own timeline.
This is also the point where acclimation stops being a one-off event and becomes part of your ongoing record. Logging the acquisition date, dip product used, placement and first observations gives you a baseline to compare against later — and pairing that entry with your parameter history is how you tell the difference between a coral struggling with your tank's chemistry and one still working through a normal, temporary acclimation stress.
Log every new coral in ReefDeck
ReefDeck is a free, offline reef logbook. Note the acquisition date, placement and first observations for every coral, then watch how it settles in against your parameter trends — no account, and your data stays yours.
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How long should coral acclimation take?
Budget roughly 15–20 minutes to float the sealed bag for temperature, then 30–60 minutes of drip acclimation for salinity and pH, then a short dip per the product's instructions. The whole process typically runs 1–2 hours from bag to placement.
Do I need to dip every new coral?
Dipping is strongly recommended for every new coral, including frags from trusted sources, since pests can hitchhike on healthy-looking tissue. It is a short, low-effort step compared with the time it takes to eradicate an established pest outbreak later.
Should I acclimate corals to light as well as water chemistry?
Yes. Place new corals low and in shaded flow for the first several days, then raise them toward their target position over 2–4 weeks based on how they respond. Full display lighting on day one is a common cause of tissue bleaching in freshly arrived corals.
Why did my newly acclimated coral close up and stay closed?
Some polyp retraction for a day or two after acclimation and dipping is a normal stress response. If a coral stays closed well beyond that, check it against your recent parameter log for a swing in alkalinity, salinity or temperature around the time it was added, since acclimation stress and a chemistry problem can look identical from the outside.