How to Acclimate New Fish and Quarantine Them

Before you bring fish home

• The tank must be ready. Cycle it first, and know your water.
• Look at the whole shop tank. A trade association says not to buy a healthy-looking fish if sick fish share its tank, because some disease shows no signs.
• Ask for the right bag. A welfare charity suggests about 2/3 air and 1/3 water, without overcrowding, and paper wrapping in cold weather.
• Go straight home. The same charity says to take the fastest route.
• Do not buy too many. A veterinary manual says it is best to add fish gradually, 1 or possibly 2 at a time, so the filter’s bacteria can keep up.

From bag to tank

The floating method

1. Turn the lights off

   A welfare charity says to do this before you start, and a veterinary manual notes that most fish rest within minutes of the lights going out.

2. Float the sealed bag

   This lets the temperature in the bag match the tank. A veterinary manual warns that adding fish directly can cause shock and stress. Keep the bag out of the sun.

3. Wait

   Sources differ. A veterinary manual says 20 to 30 minutes, a welfare charity half an hour, a trade association at least 10 minutes, and one retailer 10 to 15. We suggest the veterinary figure.

4. Mix in tank water, if your water differs

   Some sources add this step. A trade association adds tank water to the bag slowly for up to 20 minutes. A veterinarian quoted by a pet health site says the whole process should take about an hour. A veterinary manual and a welfare charity only float the bag.

5. Net the fish across

   Move the fish into the tank and throw the bag water away.

The drip method

A trade association calls this ideal for sensitive species or very different water. A magazine says it is often the best option for sensitive shrimp.

1. Match the temperature first

   Float the bag as above.

2. Pour animals and their water into a bucket

   Use a small, dark, clean one set up below the tank.

3. Start a siphon

   Clip airline tubing inside the tank with its end a few inches under water, and clip the other end to the bucket. Do not get tank water in your mouth.

4. Slow it down

   Tie a knot in the tubing, or use a small clamp, until you see 1 to 2 drips per second.

5. Wait until the waters match

   The magazine says a couple of hours is likely, and compares the two waters with a TDS (total dissolved solids) meter. If you have no meter, a kit reading for GH or pH can show the same gap. That last point is our suggestion.

6. Net the animals across

   Move the animals, not the bucket water.

Net or pour?

Net. A veterinary manual says never to let bag water into the aquarium. A welfare charity and a veterinarian say the same. A magazine lists waste and pest snail eggs among the reasons. If fish are hard to catch in the bag, it suggests pouring them through a large net over a bucket, then lowering the net into the tank.

The first day

• Lights. Sources differ: a veterinary manual turns them on again after several minutes, a magazine waits an hour or two, and a welfare charity leaves them off until the next morning. Keeping them off longer is the gentle choice.
• Food. A pet health site says it is better to underfeed during the first week.
• Bullying. A veterinary manual suggests rearranging decorations while the bag floats, feeding the other fish as you release the new one, or releasing it in the dark. A clear divider can help if aggression continues.

Quarantine basics

Quarantine means keeping new animals in a separate tank for a set time before they join others. A university guide explains why: the stress of transport can bring out disease in a fish that looks well, and at warm tropical temperatures it often shows 1 to 3 weeks after shipping.

How long. Sources agree on the minimum more than on the maximum:

• 30 days is the minimum, longer if needed, says a veterinary manual, and a university guide agrees.
• The manual’s owner edition says valuable fish should have at least 30 to 60 days.
• One retailer counts 4 to 6 weeks from the last symptom or death.

Add a new fish partway through, and the clock restarts.

A veterinary manual also says quarantine does not catch every disease. It works best for external parasites and some internal ones, so it reduces the risk rather than removing it.

A simple quarantine setup

1. Seed the filter first

   Before you buy fish, run the disinfected sponge in an established, disease-free tank, so it carries the bacteria. The quarantine tank then has a working filter on day one.

2. Watch daily

   Look for lethargy, not eating, odd breathing, spots, sores, loss of color and strange swimming.

3. Test the water

   A small new setup can go wrong quickly. Follow the ammonia steps in our cycling guide if a reading shows.

4. Clean up afterward

   A veterinary manual says to disinfect the tank and equipment and store them dry until you need them again.

Quarantine shrimp, snails and plants too, where you can. A university guide says all animal and plant life should be quarantined, because disease can travel on plants and decorations. Find shrimp and snails that suit your water in our invertebrate list.