Float the bag for temperature — always. Then it depends on where the fish came from. Short trip from a local shop: net it across, there is nothing else to equalize. Long transit or mail order: do not drip — get the fish out of the bag water quickly, because the ammonia in it turns toxic as the pH rises, by a factor of about 15. Drip only when the water is genuinely different — shrimp, marine, a big hardness gap — and drip into clean water, not into the shipping bag.
Drip acclimation is one of the few procedures in the hobby with a universally agreed method and almost no scrutiny of whether the method works. The recipe is always the same: siphon tank water through airline tubing at a couple of drops a second, wait half an hour to an hour, net the fish across. It sounds careful, it feels responsible, and for a whole class of fish it is actively the wrong thing to do.
Two sums explain why. Neither is difficult and neither appears in any ranking page on the subject.
Acclimation is two jobs, and they are not the same
Lumping them together is where the confusion starts:
- Temperature. Always matters, always worth doing, costs fifteen minutes and no thought. A bag floating in the tank equalizes on its own.
- Water chemistry. Matters when the water is genuinely different — different hardness, different salinity, different pH. That is what a drip is for: giving the fish's osmotic regulation time to follow the change rather than being hit with it.
The second one is conditional, and that is the part the standard advice drops. A fish that has travelled twenty minutes from a shop on your own municipal supply has essentially no chemistry to acclimate to. A shrimp arriving from a breeder on remineralized RO water at half your GH has a great deal. Same procedure, wildly different value.
The trap in a shipped bag
Here is the part that reverses the advice rather than just qualifying it.
A fish in a sealed bag respires. Ammonia accumulates — that part everyone knows — but so does carbon dioxide, and dissolved CO₂ makes water more acidic. So a bag that has been in transit overnight arrives acidic, and at that low pH almost all of the accumulated ammonia sits in the ionized form, NH₄⁺, which is comparatively harmless. The fish has been traveling in water that reads alarmingly on an ammonia test and is not, yet, doing much harm.
Open the bag and the CO₂ begins leaving within minutes. The pH climbs back up. And the ammonia converts:
| pH in the container | Toxic fraction | Free NH₃-N | Verdict |
|---|---|---|---|
| 6.6 | 0.23 % | 0.0037 mg/L | under the long-term guideline |
| 7.0 | 0.56 % | 0.0093 mg/L | under the long-term guideline |
| 7.4 | 1.4 % | 0.0231 mg/L | over the long-term guideline |
| 7.8 | 3.45 % | 0.0568 mg/L | into acute harm |
| 8.2 | 8.25 % | 0.1356 mg/L | into acute harm |
A bag carrying 2 ppm of total ammonia at 25 °C, computed by this site's engine as the pH rises from a transit-acidified bag toward normal tank water. Thresholds are the 0.02 mg/L long-term and 0.05 mg/L acute NH₃-N guidelines — see the parameters chart for where they come from.
The same water, the same fish, the same ammonia reading: 0.0037 mg/L of actual toxin at bag pH, 0.057 mg/L once the pH has met your tank. That is 15×, and it crosses from a non-event to acute harm on the way.
This is the bit that matters, and it is easy to miss. The pH rise is driven by CO₂ leaving the water, not by dilution — and that happens within minutes of opening the bag, in an open container, whatever your drip is doing. So dripping slowly does not make the transition gentle. It makes the fish sit in the result of it for an hour instead of thirty seconds. The one thing a slow acclimation is supposed to buy you is the one thing it cannot buy here.
Does the drip do anything?
Now the other sum. A drop is about 0.05 mL, so the universally recommended "two to three drops per second" is 6–9 mL a minute. Against a shipping bag holding a few hundred millilitres, that is less than it sounds:
| Drip rate | Added in an hour | Bag water left after an hour | Time to reach 25% bag water |
|---|---|---|---|
| 1 drop/sec | 180 mL | 69% | 6.7 hours |
| 2 drops/sec | 360 mL | 53% | 3.3 hours |
| 3 drops/sec | 540 mL | 43% | 2.2 hours |
| 4 drops/sec | 720 mL | 36% | 1.7 hours |
Computed for a 400 mL bag — a typical small-fish bag — by this site's engine. Dilution here is bag ÷ (bag + added): nothing is removed, so the original water is spread through a growing volume rather than replaced, and each further halving costs as much water as everything added so far.
Read the third column against what the same articles claim. At the standard 2 drops per second for an hour, the fish is still sitting in 53% bag water at the moment acclimation is declared complete. At the fastest rate anyone recommends it is 36%. The procedure does not do what it is described as doing.
The "let it double, throw half away, let it double again" protocol is the honest version — two rounds really does leave 25% bag water — but nobody prints how long it takes. On this bag at 2 drops per second it is 2.2 hours, not the thirty to sixty minutes quoted a paragraph earlier in the same guides. A large bag at a slow drip is 8.9 hours. Meanwhile the pH has been at tank level since the first ten minutes.
What to actually do
| Where it came from | What's actually different | Do this |
|---|---|---|
| Local shop, short trip, similar water | Temperature, and not much else. | Float 15–20 min, net the fish across, discard the bag water. |
| Local shop, very different water | Hardness or pH, with little ammonia — the trip was short. | Float, then drip 30–60 min. This is the case the standard advice was written for. |
| Mail order, overnight or longer | Ammonia, urgently. Chemistry, secondarily. | Float for temperature. Then net the fish straight out into clean tank-temperature water. Do not drip in the bag water. |
| Shipped shrimp, or a big hardness gap | Both, pulling in opposite directions. | Net into a clean container of tank-temperature water first, then drip into that. You get the gradual change without the ammonia. |
| Fish visibly distressed in the bag | Whatever it is, time is not helping. | Straight into the tank. A bad transition beats a long exposure. |
The fourth row is the resolution of the whole conflict, and it is worth stating on its own: the two goals only fight each other if you drip into the shipping water. Move the fish into clean water at the right temperature first, and then you can take as long as you like.
How to drip, when you should
- Float first, sealed, for 15–20 minutes. Temperature is the one thing you always equalize and the one thing the bag does for you.
- Decide using the table above before you open anything. If you are dripping, get a clean container ready — a bucket kept for this and nothing else.
- Start with a shallow container and enough water to cover the fish comfortably. Deep and narrow beats wide and shallow for keeping a small volume warm.
- Siphon with airline tubing, flow set by a knot or a cheap valve. Aim for a rate that will actually double your volume in the time you intend to spend — the table above is the reality check.
- Keep it warm. A bucket on the floor loses heat fast, and an hour of careful chemistry undone by a five-degree drop is a bad trade. Sit it in the tank, or beside a heater.
- Net the fish across. Never pour.
- Lights off for a few hours afterwards, and no food until the next day.
Never add the bag water
This is the one piece of universal acclimation advice that survives scrutiny completely intact. Bag water carries whatever the shop's system carried — parasites, medication residue, copper — plus the ammonia the fish has been producing all the way home. There is no upside. Net the fish out and pour the rest down the sink.
That applies to the acclimation container too. Once you have dripped for an hour, that bucket is diluted bag water; it is not something to tip into the display because it seems wasteful to throw away.
What you'll be told, and what's true
- "Always drip acclimate — it's the safest method." Safest for a real difference in water chemistry, on a fish that has not been in a bag long. On an overnight shipment it is the least safe common option, because it holds the fish in ammonia that your own acclimation has just made toxic.
- "Slower is gentler." Only for the change that dilution actually controls. The pH rise that matters here is driven by CO₂ leaving an opened container, and it happens on its own schedule — going slower just extends the exposure.
- "Float the bag, then open it and add tank water to the bag." Common, and poor. A floating bag has no meaningful gas exchange, you cannot see the fish properly through it, and you end up netting out of a wobbling plastic bag full of water you were trying to get rid of. Use a container.
- "Thirty minutes of dripping means the fish is in your water now." At the drip rates everyone recommends, half an hour on a 400 mL bag leaves roughly 69% of it still bag water. If you want the number to mean something, measure the volume you are adding rather than counting drops.
Common questions
How long should I float the bag?
About 15–20 minutes for a small bag, longer for a large heavy one — a big bag of water takes far more than twice as long as a small one to reach tank temperature. The honest check is to feel both, or hold a thermometer against the bag. What floating longer does not do is make anything else safer: once the bag is open, time is working against you, not for you.
Do shrimp actually need drip acclimation?
Shrimp are the clearest case for it, because the parameter that matters to them — GH, which they build shells from — often differs a lot between a shop's water and yours, and a sudden change can trigger a failed molt. But the same trap applies: if they arrived by post, get them out of the shipping water first into clean water at tank temperature, and drip from there. Drip acclimating in the shipping water is the worst of both worlds.
Should I add a dechlorinator or ammonia binder to the acclimation container?
In this one situation, yes — a product that binds ammonia is genuinely useful in an acclimation container, because it neutralizes the exact hazard the rising pH is creating and you are only there for twenty minutes. Note this is the opposite of the advice for a cycling tank, where binding ammonia hides the reading you need to see. Different job, different answer: here you are protecting one fish for a short time, not trying to measure anything.
The fish came from a local shop with the same tap water as mine. Do I need to acclimate at all?
Barely. If the shop is on the same municipal supply and the fish has been in the bag for twenty minutes, there is almost nothing to equalize except temperature — float the bag, net the fish across, done. Most of the acclimation ritual is aimed at differences that a short local trip simply does not create.