Adding a new fish to your display tank is exciting, but it’s also one of the riskiest moments for your reef or freshwater system. A simple quarantine setup dramatically reduces the chance of introducing parasites, disease, or pests that can wipe out years of hard work. Learning how to quarantine new fish properly is one of the best long-term investments you can make in your aquarium hobby.

Why You Should Always Quarantine New Fish

Even healthy-looking fish from reputable stores can carry hidden issues. Common problems include:

• External parasites like ich (white spot) and flukes
• Bacterial infections that spread quickly in closed systems
• Internal worms that cause weight loss and poor appetite
• Stress from shipping that weakens the immune system

A quarantine tank (QT) gives you time to observe, treat, and fatten up new arrivals before they join your main display. It also lets you control medication and salinity without affecting sensitive corals or invertebrates. If you’re building a full system from scratch, you may also want to read our guide on setting up a reef tank to plan ahead for quarantine space.

Setting Up a Simple and Effective Quarantine Tank

Your quarantine tank doesn’t need to be fancy. In fact, simple is better and easier to keep clean.

Basic Equipment Checklist

• Tank: 10–20 gallons for most small to medium fish; larger species need more volume.
• Filter: Sponge filter or hang-on-back filter with seeded biological media.
• Heater & thermometer: Stable temperature is critical for recovery.
• Hiding spots: PVC elbows, plastic plants, or ceramic caves (easy to disinfect).
• Cover: A tight lid or mesh top to prevent jumping.
• Light: Simple, low-intensity light; bright lighting increases stress.

Use bare bottom for easy cleaning and to monitor waste. Before bringing home a new fish, run the quarantine tank with a cycled sponge or media from your established system. For help with this, check out our article on how to cycle an aquarium.

Quarantine Timeline and Daily Routine

A typical quarantine period is 4–6 weeks, depending on the species and any issues you observe.

• Days 1–3: Focus on stress reduction. Dim lights, provide hiding spots, and offer small, frequent meals.
• Daily: Check appetite, breathing rate, fins, and body for spots, redness, or scratching behavior.
• Every 1–2 days: Test ammonia, nitrite, nitrate, and pH; perform small water changes as needed.
• Throughout quarantine: Keep a simple log of behavior, treatments, and water parameters.

Pro tip: Feed a variety of high-quality foods—pellets, frozen, and algae-based options—to build up the fish’s strength and immune system during quarantine.

When and How to Treat During Quarantine

Some hobbyists prefer a proactive treatment plan, while others treat only if symptoms appear. Whichever you choose, quarantine makes treatment safer and more controlled.

• Observe first: Spend a few days just watching the fish before adding any medication.
• Targeted treatment: If you see white spots, heavy breathing, or flashing, consider appropriate parasite treatments.
• Internal issues: Stringy feces or weight loss may call for medicated food.
• After treatment: Run fresh carbon and perform water changes before transferring the fish to your display.

Before moving the fish, ensure your display tank is stable and mature. If you’re still in the planning phase, our overview of common beginner aquarium mistakes can help you avoid setbacks.

Quarantine might feel like an extra step, but it quickly becomes a routine part of responsible fishkeeping. By giving every new fish a safe, controlled start, you protect your display, reduce losses, and ultimately enjoy a healthier, more stable aquarium for years to come.