How to Quarantine New Fish: Step-by-Step Guide

Every experienced fishkeeper has a story about the time they skipped quarantine. A beautiful new fish goes straight into the display tank, and within days the entire community is battling ich, velvet, or something worse. Quarantine is not glamorous, and it delays the gratification of seeing your new purchase in its intended home — but it is the single most effective way to protect your existing livestock from disease, parasites, and unexpected aggression.

This guide covers everything you need to know about setting up and running an effective quarantine process, from the bare-bones tank setup to medication protocols and the specific considerations for quarantining plants and shrimp.

Why Quarantine Matters

Fish from local shops and online sellers have been through a chain of stress — collection or breeding, packaging, transport across borders, holding in wholesale facilities, and finally retail display. At each stage, they are exposed to new pathogens and weakened by stress. A fish that looks healthy at the shop may be carrying ich cysts, internal parasites, or bacterial infections in their early, invisible stages.

Without quarantine, you introduce these risks directly into your established tank, where your existing fish — who have never been exposed to these specific pathogens — are vulnerable. An outbreak in a fully stocked, elaborately aquascaped display tank is vastly harder to treat than in a simple quarantine setup. Medications can harm plants, kill beneficial bacteria, and stain silicone. In a quarantine tank, none of that matters.

Even if the new fish appears perfectly healthy, quarantine gives you time to observe baseline behaviour, ensure it is eating properly, and catch subtle signs of illness before they become full-blown problems.

Quarantine Tank Setup

A quarantine tank does not need to be fancy. In fact, simpler is better — you want easy cleaning, full visibility, and no materials that absorb medication. Here is the minimal setup:

Tank: A 20–40 litre tank is sufficient for most community fish. For larger species, size up accordingly. A clear plastic storage container also works in a pinch.
Filter: A small sponge filter connected to an air pump is ideal. Sponge filters provide biological and mechanical filtration without strong flow that might stress weakened fish. Keep a spare sponge filter running in your main tank at all times so it is pre-seeded with beneficial bacteria when you need it.
Heater: In Singapore’s tropical climate, a heater is often unnecessary — room temperature typically keeps water at 27–30 degrees Celsius. However, if your quarantine tank is in an air-conditioned room, use a small adjustable heater set to 28 degrees.
Hiding spots: A few PVC pipe offcuts or a terracotta pot provide shelter and reduce stress. Avoid driftwood and porous rocks — they absorb medications and are difficult to sterilise between uses.
Lighting: Ambient room lighting is sufficient. Strong lighting adds unnecessary stress.
No substrate: A bare-bottom tank is easiest to keep clean and lets you spot uneaten food, faeces, and parasites immediately.

Maintain the quarantine tank with daily 20–30% water changes using dechlorinated water matched to the tank temperature. Singapore’s tap water contains chloramine, so always use a quality water conditioner like Seachem Prime.

How Long to Quarantine

The minimum recommended quarantine period is two weeks. Three to four weeks is safer and catches slow-developing conditions. Here is why:

Ich (white spot disease) has a lifecycle of 3–7 days at tropical temperatures. Two weeks covers multiple lifecycle completions, ensuring any dormant cysts have hatched and been treated.
Velvet can take 10–14 days to present visible symptoms.
Internal parasites may take two to three weeks to show signs like white stringy faeces, weight loss, or lethargy.
Bacterial infections typically manifest within the first week if the fish is carrying them.

If you medicate during quarantine (see below), the clock resets after treatment ends — observe for at least one additional week of clean health before transferring.

Daily Observation Checklist

Check your quarantined fish daily for the following. Keep a simple log — even notes on your phone — so you can track changes over time:

Appetite: Is the fish eating enthusiastically? Refusing food is often the first sign of illness.
Body condition: Look for white spots, gold dust (velvet), cottony patches (fungus), red streaks, raised scales (dropsy), or fin erosion.
Fins: Are fins held erect and spread, or clamped tightly against the body? Clamped fins indicate stress or early disease.
Breathing: Rapid gill movement or gasping at the surface suggests gill parasites, low oxygen, or ammonia issues.
Swimming: Normal, active swimming is a good sign. Flashing (rubbing against surfaces), spinning, listing to one side, or hovering near the bottom are red flags.
Faeces: Healthy faeces are dark and solid. White, stringy, or translucent faeces suggest internal parasites.
Skin: Excess mucous production (slimy appearance), discolouration, or lesions warrant investigation.

For a detailed guide on identifying specific conditions, see our article on common fish diseases and treatments.

Medication Protocol

There are two approaches to quarantine medication: reactive (treat only if symptoms appear) and prophylactic (treat preventatively regardless of symptoms). Most experienced hobbyists in Singapore lean toward a prophylactic approach, especially for wild-caught fish and imports from Southeast Asian farms.

Prophylactic Treatment (Recommended)

A standard prophylactic protocol uses three medications in sequence:

Week 1: Anti-parasitic. Treat with a broad-spectrum anti-parasitic such as praziquantel (PraziPro) to address internal worms and gill flukes. Dose as directed for 5–7 days.
Week 2: Anti-bacterial. Follow with a bacterial treatment such as a combination of kanamycin and nitrofurazone (Seachem KanaPlex and API Furan-2). This addresses potential bacterial infections that may not yet be visible.
Week 3: Observation. No medication. Watch for any remaining symptoms. If the fish is eating, active, and shows no signs of disease, it is ready for transfer.

Some hobbyists add a round of ich treatment (malachite green and formalin, or heat treatment at 30 degrees Celsius) during week one. This is especially prudent for fish sourced from crowded retail tanks where ich is endemic.

Reactive Treatment

If you prefer not to medicate healthy-looking fish, simply observe for the full quarantine period and treat only if symptoms appear. This approach is reasonable for captive-bred fish from reputable local breeders, where disease risk is lower.

Medication Availability in Singapore

Most common aquarium medications are available at well-stocked local fish shops and online retailers. Seachem, API, and Hikari products are widely carried. Prescription antibiotics like erythromycin and metronidazole may require sourcing from specialist shops. Always check expiry dates and follow dosing instructions precisely — overdosing in a small quarantine tank is a common and dangerous mistake.

Feeding During Quarantine

Newly acquired fish may refuse food for the first one to three days due to stress. This is normal — do not panic or attempt to force-feed. Offer small amounts of high-quality food once or twice daily. Remove uneaten food after five minutes to prevent ammonia spikes in the bare-bottom quarantine tank.

Good quarantine foods include:

High-quality pellets or flakes (Hikari, New Life Spectrum)
Frozen bloodworms or brine shrimp — usually irresistible to reluctant eaters
Blanched vegetables for herbivorous species

If a fish refuses all food for more than five days, it likely has an underlying health issue. Begin treatment or consult an experienced fishkeeper.

When to Add Fish to the Main Tank

Transfer quarantined fish to your display tank when all of the following conditions are met:

The full quarantine period (minimum two weeks, ideally three to four) has elapsed.
Any medication course has been completed, followed by at least one week of symptom-free observation.
The fish is eating enthusiastically and showing normal, active behaviour.
No visible signs of disease — no spots, clamped fins, excess mucous, or abnormal faeces.

When transferring, float the bag or container in the display tank for 15–20 minutes to equalise temperature, then gradually add small amounts of display tank water over 30–60 minutes. This is especially important if there is a pH or hardness difference between the quarantine and display tanks. Net the fish into the display tank and discard the quarantine water — do not pour it into the main tank.

Quarantining Plants

New aquatic plants can carry pest snail eggs, algae spores, planaria, hydra, and even fish disease pathogens. While plant quarantine is less critical than fish quarantine, it is worth doing if you want to avoid introducing hitchhikers.

Options for plant quarantine:

Alum dip: Dissolve 1–2 tablespoons of alum (potassium aluminium sulphate, available at baking supply shops) per litre of water. Soak plants for 2–3 hours. This kills snails, snail eggs, and many invertebrate pests without harming most plants.
Potassium permanganate dip: Prepare a light pink solution and soak plants for 10–15 minutes. Rinse thoroughly afterwards. Effective against parasites and algae.
Bleach dip: A 1:19 ratio of household bleach to water for 60–90 seconds kills virtually everything, but also damages delicate plants. Use only on hardy species like Anubias and Java fern. Rinse immediately and soak in dechlorinated water with double-dose conditioner.
Quarantine tank: Keep new plants in a separate container with light for one to two weeks. Inspect for snails, planaria, and algae before adding to your display.

Tissue-cultured plants (sold in sealed cups of gel) are guaranteed pest-free and parasite-free. They cost slightly more but eliminate quarantine concerns entirely. These are available at most aquascaping shops in Singapore.

Quarantining Shrimp

Shrimp are more sensitive than fish to water chemistry changes and medications. Quarantine them separately from fish, and never expose them to copper-based medications or salt treatments above 1 ppt.

For shrimp quarantine:

Use a small cycled tank with a sponge filter and a few moss clumps for biofilm grazing.
Match water parameters (pH, GH, KH, TDS, temperature) as closely as possible to the supplier’s conditions, then gradually adjust toward your display tank parameters over the quarantine period.
Observe for two to three weeks. Watch for lethargy, failed moults, white or opaque patches (bacterial infection), or green/brown internal discolouration (parasitic infection).
Avoid medicating shrimp prophylactically. Most fish medications are lethal to invertebrates. If treatment is needed, research shrimp-safe options carefully.

Frequently Asked Questions

I do not have space for a permanent quarantine tank. What can I do?

A quarantine tank does not need to be permanent. A 20-litre plastic container stored under your bed or in a storeroom works fine. Keep a spare sponge filter running in your main tank at all times — when you need to set up quarantine, simply move the sponge filter to the container, fill with dechlorinated water, add a heater if needed, and you are ready within minutes.

Can I quarantine multiple species together?

You can quarantine multiple fish from the same batch and source together, as they have been exposed to the same pathogens. Avoid mixing fish from different sources in the same quarantine tank — if one group carries a disease, you expose the other group unnecessarily.

Do I need to quarantine fish from a trusted local breeder?

The risk is lower, but quarantine is still recommended. Even a trusted breeder’s fish pass through nets, bags, and transport — all stress factors that can trigger latent infections. Two weeks of observation costs little and protects a lot.

What if a fish gets sick during quarantine?

This is exactly why you quarantine. Identify the condition, begin appropriate treatment, and continue the quarantine until the fish has been symptom-free for at least one week after completing medication. If a fish dies during quarantine, sterilise the tank with dilute bleach solution, rinse thoroughly, and start fresh before quarantining any new arrivals.

Quarantine is the cheapest insurance policy in the aquarium hobby. A S$20 plastic tub and a sponge filter can save hundreds of dollars in livestock and medication. If you are adding new fish to an established system and want professional guidance, contact the Gensou team. We offer ongoing maintenance services that include health monitoring and disease management for your entire collection.

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