Drip Acclimation, Step by Step (Fish & Inverts)

Acclimation is the unglamorous ten minutes that decides whether the animal you just bought lives to see week two. The water in a transport bag and the water in your tank differ in temperature, salinity, and pH — sometimes dramatically — and marine animals, especially invertebrates, handle abrupt chemistry changes poorly. Drip acclimation equalizes those differences slowly enough for the animal's physiology to keep up.

Here's the complete protocol: the gear, the steps, the timing per animal type, and the two cases where slower is actually worse.

Why dripping, specifically

The old "float the bag, dump it in" routine handles exactly one variable — temperature. It ignores salinity, which is the one that kills. Store and shipper water routinely sits anywhere from 1.020 to 1.026 SG, while your reef runs 1.025–1.026; a snail or shrimp moved abruptly across that gap suffers osmotic shock, and inverts have essentially no tolerance for it. Fish are tougher but not immune — abrupt transfers stress fish that were already stressed by the ride home.

Dripping tank water into the transport water raises salinity (and equalizes pH and temperature) gradually — a rate the animal's osmoregulation can track. It's the difference between wading into a cold pool and being thrown in.

First, measure the gap. When the bag is opened, test its salinity against your tank's with a calibrated refractometer. This one reading tells you how careful to be: a 0.001 difference is a short, casual acclimation; a 0.005 difference means the full slow protocol, especially for inverts.

The gear (about $10 total)

• Airline tubing, 4–6 feet
• A flow control: a plastic airline valve, or simply a loose knot in the tubing
• A clean bucket or specimen container — used for fish only, never soap
• A clip or clothespin to anchor the tubing in the tank
• Your refractometer

Commercial acclimation kits bundle exactly this for a few dollars more. Fine either way.

The protocol, step by step

1. Lights off. Turn off the tank lights (and dim the room if you can) before starting. New arrivals are stressed; darkness lowers the temperature of the whole event, including for the residents who'll meet the newcomer.
2. Float the sealed bag for 15 minutes. This equalizes temperature while you set up. In winter, this step matters more than people think — a bag that crossed a cold parking lot can be several degrees down.
3. Move animal and bag water to the bucket. Open the bag and gently pour animal and water into the bucket, tilted so the animal stays submerged — there should be enough water to cover it. Test this water's salinity now and note the gap.
4. Start the siphon. Clip one end of the airline in the tank, suck briefly on the other end to start the flow, then set your valve or knot to a drip of roughly 2–4 drips per second for fish, 1–2 drips per second for inverts. The bucket sits below the tank; gravity does the rest.
5. Drip until the volume has roughly tripled. For fish, 30–45 minutes gets you there. For inverts, aim for 60–90 minutes at the slower rate. If the bucket fills early, discard half the water and continue — this also keeps the math honest.
6. Verify. Test the bucket's salinity. When it's within 0.001 of the tank, you're done. This is the step that makes it a protocol instead of a ritual.
7. Transfer the animal, not the water. Net the fish (or lift the snail/coral by hand — dry hands off afterward) and place it in the tank. Bag and bucket water never enters your display — it carries the accumulated waste of transport and, potentially, parasites and medications from the store's system.
8. Leave the lights off for a few hours and resist feeding for the first day. Expect hiding; a new fish that spends day one behind the rockwork is behaving normally.

For fish, note that the destination should usually be your quarantine tank rather than the display — acclimation and quarantine are two halves of the same arrival protocol, and our quarantine tank setup guide covers the second half.

Timing by animal

• Fish: 30–45 minutes. Beyond an hour adds stress, not safety (see below).
• Shrimp, crabs, snails: 60–90 minutes, slow drip. Inverts are the entire reason this protocol exists — a cleaner shrimp dumped across a salinity gap can die within hours, and mysterious first-week snail deaths are usually acclimation failures. Details on the crew itself are in our cleanup crew stocking guide.
• Corals: 20–30 minutes of dripping is plenty — corals care less about small salinity steps than fish-keepers assume. Their arrival protocol is really about temperature plus a pest dip; a proper coral dip between acclimation and tank entry matters far more than an extra hour of dripping.
• Anemones and sensitive inverts (later in your hobby): the full 90 minutes, slowest drip, no shortcuts.

The two cases where slower is worse

1. Long-shipped bags (overnight fish in sealed bags). During a long transit, CO₂ accumulates and pH drops in the bag — but the dissolved ammonia stays in its less-toxic form because the pH is low. The moment you open the bag and fresh air hits the water, pH rises and that ammonia converts toward its toxic form with the fish still sitting in it. For bags that traveled 12+ hours: float briefly for temperature, then get the fish out of that water on an accelerated schedule — a shortened 15–20 minute drip, or for visibly stressed fish, a direct transfer after temperature equalization if salinities are close. An ammonia-detoxifier drop added to the bag water at opening buys time.

2. Gasping, laid-over, or clearly crashing animals. A fish in visible distress needs stable tank water more than it needs a gentle gradient. Match temperature, do a token drip if salinity allows, and transfer. Perfect is the enemy of alive.

The habits that make arrivals boring

Done right, acclimation is uneventful — the drama was removed in advance. Keep a permanent acclimation kit (tubing, valve, dedicated bucket) with your fish gear; test the bag and the tank every time rather than assuming; buy from sources that keep salinity near reef-normal; and put arrivals on days when you have ninety unhurried minutes. Losing an animal you chose carefully to a preventable ten-minute shortcut is the particular flavor of regret this hobby teaches exactly once.

Acclimation is one link in the arrival chain — choose hardy species, quarantine fish, dip corals, acclimate everything slowly. The full chain, in order, is in our beginner's guide, The First Tank.

FAQ

Do I really need to drip acclimate snails and hermit crabs?

Yes — more than anything else you'll buy. Invertebrates cannot regulate internal salinity the way fish partially can, and osmotic shock from a quick transfer is the leading cause of "my snails died in the first week." Ninety slow minutes is the difference between a crew that lasts years and one that lasts days.

Can I just float the bag for 15 minutes like the store told me?

Floating equalizes temperature only. If the store's salinity happens to match yours (test it!), a float-and-transfer is survivable for hardy fish. But you won't know until you measure, and inverts fail this shortcut routinely. The drip method costs $10 and 45 minutes; it removes the gamble entirely.

Should acclimation water go into my tank?

Never. Transport water contains concentrated waste, possible medications (many stores run copper in fish systems — lethal to your inverts), and potentially parasites. Net or hand-lift the animal across; pour the water down the drain.