How to Add New Fish to Tank: Step-by-step Safety Guide

Adding new fish to a fish tank is a relatively straightforward process, but it must be done carefully each and every time. Whether you are introducing newly bought fish or moving one from a quarantine tank to a display tank, they need time to adapt.

Here’s how to add new fish to a tank in a nutshell:

1. Open the transportation bag.
2. Float it in the aquarium but make sure no water enters.
3. Secure the bag at the edge of the tank with a laundry pin so it doesn’t leak its contents into the tank.
4. Keep it like this for 20 minutes so the bag’s water acquires the same temperature as the aquarium water. Otherwise, the fish can suffer temperature shock.
5. Every 4-5 minutes pour some water from the tank into the bag. By the 20th minute, the bag should contain 65%-75% aquarium water. This will prevent pH shock in the new fish; sensitive species, shrimp, and marine should undergo drip acclimation.
6. After 20 minutes have elapsed, remove the transportation bag from the tank, catch the fish with a net, and add them into the aquarium. Discard the bag and its water.
7. In case the procedure has lowered the water level of your tank too much, top it up with dechlorinated water, as you normally would upon a regular water change or top-up.

Now, these steps are literally it.

If you don’t want to read me nerding it out on the intricacies of introducing new fish or shrimp to a tank, just follow these steps and your fish will be fine. If nerding it out is your thing, read on!

Should I Always Acclimate Fish?

Every time a fish is moved from one aquarium to another, it should be acclimated. Moving fish from one tank to another causes disturbingly high death rates in the hobby. Simple precautions and adherence to the above protocol largely eliminate the risk.

Even if you are moving fish between two aquariums you own that are filled from the water source, it is practically guaranteed that the two water columns will have different water chemistry. The type and size of filter, type and amount of substrate, plants, organics or lack thereof, fish population, and tank age always create chemically unique combinations that are nigh impossible to fully replicate.

The only possible exception is when both tanks are bare bottom, undergo frequent water changes, and you know for a fact the water parameters are the same. Regular testing can verify the latter, but I’d still acclimate the fish when changing tanks.

Most water testers, especially strips, aren’t extremely accurate so it would be better to err on the side of caution and allow the fish to get used to the new tank.

pH shock is a quick killer and temperature discrepancies between the tanks can also send your fish reeling. Shrimp, especially of the Caridina family (but Neocaridina, too) are extremely sensitive to the slightest water changes, so drip acclimation is the only sensible way to go.

What about Quarantine?

Quarantine is necessary to keep your main tank healthy. New fish, especially from an unchecked source, can carry disease, while plants are the favorite mode of transportation for pest snails.

Getting rid of them isn’t always easy while introducing sickness to your main tank is never a good outcome. The standard quarantine period is four weeks, but even two weeks are much better than none.

It’s OK if you make them watch TV but from a safe distance, as quarantine tanks can be rather boring, especially for a single fishy.

Joking aside, regardless of how long you quarantine your new fish, they must be acclimated properly upon introduction into their permanent home.

Drip Acclimation for Sensitive Fish — The Best Way to Add New Fish

Sensitive species like discus must be introduced to their new world more carefully. Shrimp and marine fish should follow the procedure outlined below, too.

Drip acclimation uses a tube or siphon to transfer water from the main tank to the container with the new fish. Instead of pouring some water every few minutes, this method drips a few drops every second. It greatly reduces stress and is the safest way to introduce any newcomer to your tank.

The best part is that this way of acclimating new fish is extremely affordable and doesn’t need much monitoring at all. The standard way of pouring a bit of water every 4-5 minutes requires you to perform the action several times in 20 minutes.

With drip acclimation, you can set it up and come back after 20-30 minutes.

All you need is a couple of meters of soft plastic tube, like the one sold for air pumps in fish stores, a couple of laundry pins, and a couple of water containers.

1. Place the new fish in a bucket or another clean container with enough room for 2-3 liters of water.
2. Place the container below the aquarium.
3. Grab a narrow plastic tube, dip it into the aquarium, and secure it with a laundry pin.
4. Make a loose knot on the tube.
5. Suck on the other end to create the siphon.
6. Use the empty vessel to pour the initial flow into.
7. Regulate the strength of the flow by tightening the knot.
8. When the flow slows down to 2-4 drops per second, place the tube in the fish container.
9. Secure the tube with the other laundry pin.
10. Set a timer for 25-30 minutes.
11. When the time is up, catch the fish or shrimp with a net and add them to their new tank.

There are more advanced systems for drip acclimation than transparent tubing for air pumps. Adding an air regulator is a very easy way to regulate the water flow precisely and with minimum fuss.

Transport New Fish Quickly, Acclimate Them Slowly

Drip acclimation is by far the best way to add new fish or shrimp to your tank, but it won’t do you much good if you keep the new fish in the transportation bag for too long.

In a closed bag, the gas exchange happening on the water surface will build a high amount of CO2 that has nowhere to go. When you open the bag, the instant oxygen flow can mess up the fish completely.

In case you have to keep them in the bag for longer than two hours, open the bag so that oxygen enters freely.

The other issue with keeping fish in a bag for too long is temperature. If the weather is too hot or too cold, they will suffer as the tiny transportation bag is at the mercy of the elements.

When buying fish, plan it in such a way that will see them safely home as quickly as possible.

Then if possible, go for drip acclimation, as it is the safest way to add new fish.