Fish Care

How to Bring New Fish Home: A Step-by-Step Guide

Published on June 13, 2026 · 10 min read · By The Fisherman Team

You just bought a beautiful new fish — exciting! But the next few hours are the most critical in that fish's life. Most fish deaths that happen within the first week are not because the fish was sick. They happen because of temperature shock, pH shock, or stress caused by rushing the transfer from bag to tank.

Whether you ordered from The Fisherman and received a delivery bag, or you're carrying a plastic bag home from a local shop in Bangalore, this guide walks you through every step to give your new fish the best possible start.

Before you even buy: Make sure your aquarium has completed its nitrogen cycle and the water parameters are stable. Adding fish to an uncycled tank is the single most common reason new fish die within days. If you're not sure, test your water with an API Master Test Kit before purchasing.

What You'll Need

A separate quarantine tank (even a clean bucket or small tub works for beginners)
A clean bowl or container for the float step
A fish net (no hands — skin oils and soap residue are toxic to fish)
A water testing kit (API Master Test Kit recommended)
A thermometer
Aquarium salt (optional but useful for stress relief)

1 Do Not Open the Bag Immediately

The moment you get home, resist the urge to open the bag or pour the fish into your tank. The water inside the bag has a specific temperature and pH that your fish has adjusted to over the journey. Dumping it straight into your tank — even a perfectly set up one — causes immediate temperature and chemistry shock.

Place the sealed bag on a flat surface. Take a breath. The fish can wait 15–30 minutes — that time is exactly what's going to save its life.

Delivery tip: If your fish arrived via courier (like a The Fisherman order), check the bag for damage first. If the water looks dark brown or smells strongly of ammonia, do a quick drip acclimation — don't add any of the bag water to your tank. Ammonia builds up fast in sealed bags during long transit.

2 Float the Bag to Equalise Temperature (15–20 Minutes)

Place the sealed, unopened bag into your aquarium (or quarantine tank) so it floats on the surface. This slowly brings the bag water to the same temperature as your tank water.

Keep the bag floating for at least 15–20 minutes
For sensitive fish (discus, marines, scaleless fish), float for 30 minutes
Keep the tank light off — darkness reduces stress during acclimation
Do not let the bag sink or fall over

Temperature difference of even 2–3°C between bag and tank can cause thermal shock, weakening the fish's immune system and making it immediately vulnerable to ich and other parasites.

Indian summer tip: In Bangalore's summer months (March–May), room temperature can hit 32–35°C. If your shop bag has been in a hot auto or car, the bag water may actually be warmer than your cooled tank. The float step equalises in both directions — always do it regardless of season.

3 Drip Acclimation — Adjust to Your Water Chemistry (20–30 Minutes)

After temperature is equalised, it's time to slowly introduce your tank water into the bag water. This adjusts the fish to your tank's pH, hardness, and salinity.

Simple Method (Beginner Friendly)

Open the bag and roll down the top to create a collar so it floats upright
Every 5 minutes, use a small cup to add a little of your tank water into the bag
Do this 4–5 times over 20–25 minutes
By the end, roughly half the water in the bag should be your tank water

Drip Method (Recommended for Sensitive Fish)

Pour the bag contents into a clean bucket or bowl
Run an airline tube from your tank to the bucket — tie a loose knot in the tube to restrict flow to 2–3 drips per second
Let it drip for 30–45 minutes until the water volume doubles
Discard half the water and let it drip again for another 15–20 minutes

The drip method is strongly recommended for marine fish, discus, and any wild-caught species. For hardy community fish like guppies, mollies, or tetras, the simple cup method is sufficient.

Never pour bag water into your tank.

The water inside the transport bag can carry parasites, bacteria, or medications from the shop's system. You want the fish — not the water. Use a net to transfer the fish and discard the bag water entirely.

4 Transfer the Fish with a Net

Once acclimation is complete, use a clean fish net to gently scoop the fish out of the bag and lower it into your quarantine tank. Do this with the net partially submerged to minimise air exposure.

Work quickly but gently — the fish should spend no more than 3–5 seconds out of water
Never use your hands unless absolutely necessary
If the fish is very small or has long fins (like a betta), tilt the bowl/bag and let the fish swim directly into the tank — avoid netting altogether
Discard all the bag water — do not pour it into your tank

5 Quarantine First — Don't Add Directly to Your Main Tank

This step is skipped by most beginners and regretted by all of them. Every new fish should spend 2–4 weeks in a quarantine tank before joining your established community.

New fish from any source — shops, online sellers, even trusted breeders — can carry ich, velvet, internal parasites, or bacterial infections that show no visible symptoms for days. A single infected fish can wipe out an entire tank within a week.

Quarantine Tank Setup

A 10–20 litre tub, spare tank, or even a large clean bucket works
Add a small sponge filter or an air stone for oxygenation
Use water from your established main tank to jumpstart good bacteria
Keep it bare bottom (no gravel) — easier to spot droppings and monitor health
Maintain the same temperature as your main tank

What to Watch During Quarantine

White spots, unusual spots, or velvet-like dust on the body
Clamped fins or fins held close to the body
Rapid breathing or gasping at the surface
Scraping against surfaces (flashing)
Bloating, raised scales, or sores
Loss of appetite after the first 2 days
Stringy or white feces

If the fish looks and behaves completely normal for 3–4 weeks, it's safe to move to the main tank.

Optional prophylactic treatment: Many experienced fishkeepers treat all new fish during quarantine with a broad-spectrum medication (like PraziPro for internal parasites) as a precaution — even if the fish looks healthy. This is especially useful for fish bought from shop tanks with high stocking density.

6 Do Not Feed for the First 24 Hours

Your new fish is stressed. Its digestive system is not functioning normally right after the stress of transport and acclimation. Feeding too early causes uneaten food to rot, spikes ammonia, and stresses the fish further.

Wait at least 24 hours before offering any food
For sensitive species (discus, wild-caught fish), wait 48 hours
For the first feeding, offer a very small amount — less than you think is needed
Watch whether the fish actually eats; a fish refusing food after 48 hours is a stress or illness signal

A healthy fish will typically start showing interest in food within 1–2 days once it settles in and feels safe.

7 Keep Lights Off and Tank Calm

For the first 24 hours, minimise disturbances around the quarantine tank.

Keep aquarium lights off or dimmed for the first 12–24 hours — bright light increases stress
Avoid loud music, vibrations, or children tapping the glass
Do not rearrange decorations in the main tank the same day you plan to add the new fish — this stresses resident fish and disrupts established territories
Add some cover — a floating plant, a terracotta pot, or even a folded card over part of the tank gives the fish a hiding spot and reduces anxiety

8 Test Your Water the Next Day

Test the quarantine tank water 24 hours after adding the fish. Even a well-cycled quarantine setup can spike ammonia when a new fish is introduced.

Target Parameters (Freshwater)

Ammonia: 0 ppm (any reading above 0 is dangerous)
Nitrite: 0 ppm
Nitrate: Below 20 ppm
pH: 6.8–7.4 for most community fish
Temperature: 24–28°C for most tropical freshwater fish

If ammonia or nitrite shows any reading, do an immediate 25–30% water change with dechlorinated water at the same temperature.

Bangalore tap water note: Bangalore's BWSSB tap water is chlorinated and sometimes has elevated TDS during monsoon season. Always use a dechlorinator (sodium thiosulfate or API Stress Coat) before adding tap water to any fish tank — even just for a water change. Never use untreated tap water directly.

9 Introducing to the Main Tank

After a clean 2–4 week quarantine with no signs of disease, your fish is ready for the main tank. Don't just drop it in.

Move the fish during lights-off or in the evening — reduced light lowers territorial aggression from existing fish
Rearrange a few decorations before adding — this breaks up established territories and gives the new fish a fair chance
Watch for 30–60 minutes after introduction to spot any aggressive behaviour from resident fish
Have a backup plan — a divider or the quarantine tank — in case of severe bullying
For shoaling fish (tetras, danios, rasboras), always add at least 6 at once — lone fish get targeted

Common Mistakes That Kill New Fish

Avoid these — they are the most common reasons fish die within the first week:

Skipping acclimation entirely — dumping bag water and fish straight into the tank
No quarantine — introducing fish directly to a display tank with existing fish
Overfeeding on day one — ammonia spike from uneaten food in a stressed tank
Adding fish to an uncycled tank — ammonia accumulates with no bacteria to process it
Using cold or hot tap water for top-ups without temperature matching and dechlorination
Overcrowding — adding multiple new fish at once overwhelms even a cycled tank's biological filter
Pouring bag water into the tank — introduces shop bacteria, parasites and medications into your tank

Quick-Reference Checklist

✅ New Fish Arrival Checklist

Do not open the bag immediately
Float sealed bag in tank for 15–20 minutes
Add tank water to bag every 5 minutes for 20–30 minutes
Net the fish into quarantine tank — discard bag water
Keep lights off for 12–24 hours
Do not feed for the first 24 hours
Test water at 24 hours — target ammonia and nitrite at 0
Observe daily for disease symptoms for 2–4 weeks
Introduce to main tank after clean quarantine

When to Be Concerned

Contact your seller or a fish health consultant if you notice any of the following within the first few days:

White spots or dusty coating on fins and body (ich or velvet)
Fish sitting at the bottom, not moving, and not responding
Rapid gill movement or gasping at the surface (oxygen deprivation or gill disease)
Visible wounds, lesions, or torn fins that weren't there when you bought the fish
Complete refusal to eat after 3–4 days

The Fisherman offers live arrival support on all fish orders. If your fish arrived in poor condition, reach out on WhatsApp within 2 hours of delivery with a photo or video — we'll help you assess and make it right.

Final thought: The 30–45 minutes you spend on proper acclimation can mean the difference between a fish that lives for 5 years and one that dies in 5 days. It is the single most impactful thing a fishkeeper can do — and it costs nothing except a little patience.