How to Quarantine New Fish in a Hospital Tank

Introducing new fish to your aquarium without quarantine is like inviting strangers to a party without checking for illnesses—one sick fish can wipe out your entire tank. Quarantine tanks, also called hospital tanks, are essential for intermediate aquarists to prevent parasites, bacteria, and viruses from spreading.

In this guide, you'll learn how to set up a dedicated quarantine tank, acclimate new fish, monitor for issues, and safely integrate them into your display tank after 2-4 weeks. The process ensures healthy fish and a thriving aquarium ecosystem.

Expect 1-2 hours for initial setup, plus daily monitoring over 2-4 weeks. It's intermediate level, requiring basic knowledge of water parameters and equipment.

▸What You'll Need

• •5-10 gallon aquarium tank (glass or acrylic)
• •Adjustable aquarium heater (25-50W for small tank)
• •Sponge filter or hang-on-back (HOB) filter with mature media
• •Air pump and airline tubing (for sponge filter)
• •Aquarium light (LED preferred)
• •Water conditioner (e.g., Seachem Prime)
• •Test kit for ammonia, nitrite, nitrate, pH, and temperature
• •Gravel or bare bottom substrate (optional sand/gravel)
• •Quarantine medications (e.g., Seachem ParaGuard, API Stress Coat)
• •Siphon hose or turkey baster for water changes
• •Net and acclimation bucket
• •Thermometer

Estimated Time: 1-2 hours setup + 15 minutes daily monitoring for 2-4 weeks Difficulty: intermediate

▸Step-by-Step Instructions

Step 1: Choose and Prepare the Quarantine Tank

Select a 5-10 gallon tank dedicated solely to quarantine—never use it for your main display afterward to avoid cross-contamination. Rinse the tank thoroughly with warm water and no soap to remove dust or residues.

Place it in a stable, draft-free location near your main tank for easy parameter matching. Add a thin layer of gravel or leave bare bottom for easy cleaning.

What success looks like: Clean, empty tank ready for equipment.

💡 Tips:

• •Label the tank 'QUARANTINE' to prevent mix-ups.

⚠️ Warnings:

• •Avoid using soap or chemicals—they're toxic to fish.

Step 2: Install Heater, Filter, and Light

Install an adjustable heater set to match your main tank's temperature (typically 78-82°F for tropical fish). Add a sponge filter powered by an air pump—it's gentle and biological.

Attach the LED light on top. Plug everything into a power strip with a surge protector.

What success looks like: Equipment running, gentle water flow from filter.

💡 Tips:

• •Use mature filter media from your main tank to 'seed' beneficial bacteria.

⚠️ Warnings:

• •Test heater functionality in bucket water first to avoid burns.

Step 3: Fill and Cycle the Tank

Fill with dechlorinated water matching your main tank's parameters (use conditioner). Add bacterial starter if available.

Cycle the tank for 3-7 days: Test daily for zero ammonia/nitrite. Perform 25% water changes if spikes occur.

What success looks like: Stable parameters (ammonia 0, nitrite 0, nitrates <20 ppm).

💡 Tips:

• •Speed cycling with bottled bacteria like Seachem Stability.

⚠️ Warnings:

• •Never skip cycling—uncycled tanks cause deadly ammonia poisoning.

Step 4: Acclimate the New Fish

Float the fish bag in the quarantine tank for 15-20 minutes to match temperature. Gradually add tank water to the bag over 30-45 minutes.

This prevents shock from pH, temperature, or salinity changes.

What success looks like: Fish swimming calmly in bag with mixed water.

💡 Tips:

• •Dim lights during acclimation to reduce stress.

Step 5: Transfer Fish to Quarantine Tank

Net the fish into a bucket of tank water, discard the bag water. Gently release into the quarantine tank.

Add Stress Coat immediately to protect slime coat.

What success looks like: Fish hiding or exploring, breathing normally.

⚠️ Warnings:

• •Minimize air exposure during netting.

Step 6: Daily Monitoring Routine

Check temperature, behavior, and fins daily. Test water parameters every 2-3 days. Feed sparingly (once daily, what they eat in 2 minutes).

Perform 25-50% water changes weekly, matching parameters.

What success looks like: Consistent parameters, active fish.

💡 Tips:

• •Keep lights on 8-10 hours/day, off at night.

Step 7: Observe for Disease Signs

Watch for lethargy, flashing, white spots (ich), clamped fins, or redness. Inspect closely without stressing fish.

Quarantine for minimum 14-30 days to break parasite lifecycles.

What success looks like: No symptoms after 2+ weeks.

⚠️ Warnings:

• •Don't treat prophylactically unless experienced—stress can worsen issues.

Step 8: Treat if Needed and Integrate

If diseased, dose meds per instructions (e.g., ParaGuard for parasites). After treatment and 2 weeks symptom-free, re-acclimate to main tank.

Disinfect quarantine tank thoroughly afterward.

What success looks like: Healthy fish thriving in main tank.

💡 Tips:

• •Observe 1 week post-transfer in main tank.

▸Pro Tips

• •Match quarantine parameters exactly to main tank for seamless transfer.
• •Use a timer for lights and heater to maintain consistency.
• •Document daily logs: parameters, feeding, observations.
• •Add Indian almond leaves or chiller for natural stress relief.
• •Quarantine all new fish, even 'hardy' species.
• •Overfeed minimally—uneaten food fuels bacteria.
• •Blackout tank 1-2 days post-transfer to ease stress.

▸Common Mistakes to Avoid

• •Skipping the cycling process, leading to ammonia spikes and fish death.
• •Using the same net/gravel between tanks, spreading diseases.
• •Quarantining too short (under 2 weeks), missing parasite cycles.
• •Ignoring water changes, causing parameter drift.
• •Overmedicating without diagnosis, harming beneficial bacteria.

▸Troubleshooting

Problem: Fish gasping at surface

Solution: Check oxygen—add air stone; test ammonia (do 50% water change if >0).

Problem: White spots (ich)

Solution: Raise temp to 86°F, treat with ich medication, daily 25% changes.

Problem: Stress after transfer (hiding, not eating)

Solution: Dim lights, add hiding spots; wait 3-5 days, feed live food.

Problem: Ammonia spike

Solution: Immediate 50% water change; dose bacteria supplement.

Aqueon LED MiniBow Aquarium Kit 5 Gallon

Compact, all-in-one starter kit with filter and light—perfect for quick hospital tank setup.

Best for: Ideal for beginners needing a ready-to-use quarantine tank.

Price Range: $30-$40

Seachem Prime Water Conditioner

Removes chlorine, detoxifies ammonia/nitrite/heavy metals—instantly makes tap water safe.

Best for: Essential for every water change during quarantine.

Price Range: $10-$15

API Freshwater Master Test Kit

Accurate testing for pH, ammonia, nitrite, nitrate—prevents invisible parameter issues.

Best for: Daily/weekly monitoring in quarantine.

Price Range: $30-$35

Aquarium Co-Op Mini Sponge Filter

Gentle filtration with biological media—safe for stressed fish, easy to clean.

Best for: Primary filter for small quarantine tanks.

Price Range: $10-$15

Seachem ParaGuard

Broad-spectrum treatment for parasites, bacteria, fungus—effective without harming biofilter.

Best for: Targeted treatment during observed illnesses.

Price Range: $12-$18