How to Set Up a Hospital Tank: Quarantine and Treatment

Table of Contents

• Why Every Fishkeeper Needs a Hospital Tank
• Minimal Setup Requirements
• Choosing the Right Size
• Keeping the Filter Cycled
• Setting Up for Treatment
• Medication Protocol
• When to Return Fish to the Main Tank
• Dual Use as a Quarantine Tank
• Frequently Asked Questions

Why Every Fishkeeper Needs a Hospital Tank

A hospital tank — sometimes called a treatment tank or sick tank — is a separate, minimally equipped aquarium used to isolate and treat unwell fish away from your main display tank. It is arguably the most important piece of equipment that most hobbyists do not own until they desperately need one.

The reasons for having a dedicated hospital tank are compelling.

• Targeted treatment. Medications can be dosed at precise concentrations for the affected fish without exposing healthy tank mates, plants, shrimp or beneficial bacteria in your main tank to chemicals.
• Disease containment. Isolating a sick fish immediately reduces the risk of pathogens spreading to the rest of your stock.
• Lower medication costs. Treating a 20-litre hospital tank costs a fraction of medicating a 200-litre display tank.
• Plant and shrimp safety. Many common medications — including copper-based treatments, antibiotics and even aquarium salt — are harmful to plants, shrimp and snails. A hospital tank lets you treat fish aggressively without collateral damage.
• Observation. A bare, simple hospital tank makes it easy to observe the fish closely, monitor its eating, assess symptoms and gauge recovery.

Minimal Setup Requirements

A hospital tank should be simple. The goal is function, not aesthetics. Minimal equipment means fewer surfaces for pathogens to colonise and easier cleaning between treatments.

Essential Equipment

What You Do NOT Need

• Heater: In Singapore, ambient room temperature keeps aquarium water at 28-30 °C year-round. This is within the comfortable range for virtually all tropical species. A heater is unnecessary unless you need to raise the temperature above ambient for specific treatments (e.g., ich treatment at 30-32 °C), in which case a small adjustable heater can be added temporarily.
• Substrate: Use a bare bottom. Bare glass is easier to clean, allows you to observe droppings and uneaten food, and prevents medication from binding to substrate material.
• Bright lighting: Keep lighting dim or use ambient room light. Bright light stresses unwell fish. If the tank has a light, keep it off or on a very short photoperiod.
• Decorative hardscape: Rocks and driftwood look nice but absorb medication, harbour pathogens, and make sterilisation between treatments more difficult. Keep it simple.

Choosing the Right Size

The hospital tank should be large enough to comfortably house the fish being treated, but small enough to keep medication costs manageable and water changes practical.

For most Singapore hobbyists keeping small to medium community fish, a 20-40 litre tank is ideal. These tanks are affordable ($15-30 SGD for a basic glass tank from local shops), easy to store when not in use, and practical for water changes.

A large plastic storage container can also serve as a temporary hospital tank in a pinch. Ensure it is food-grade, has not been used with cleaning chemicals, and is positioned on a stable surface.

Keeping the Filter Cycled

The biggest challenge with a hospital tank is maintaining a cycled sponge filter when the tank is not in constant use. An uncycled filter means ammonia and nitrite will spike during treatment — adding further stress to an already sick fish.

Strategies to Keep Your Sponge Filter Ready

• Run the sponge filter in your main tank. This is the most popular method. Keep a spare sponge filter running in your display tank at all times. The sponge colonises with beneficial bacteria from the main tank’s established cycle. When you need the hospital tank, simply transfer the sponge filter. This gives you an instantly cycled filter.
• Keep a spare sponge in your main filter. If space permits, place an extra sponge or filter media in your main canister or hang-on-back filter. When needed, move it to the hospital tank’s filter housing.
• Use Seachem Prime during treatment. If you cannot pre-cycle the sponge, dose Seachem Prime daily to detoxify ammonia and nitrite while the sponge establishes bacteria. This is a workable emergency approach but not ideal for extended treatments.
• Frequent water changes. In an uncycled hospital tank, daily 30-50% water changes are necessary to keep ammonia and nitrite in check. Redose medication proportionally after each water change.

Setting Up for Treatment

When a fish needs treatment, follow this procedure to set up the hospital tank quickly and correctly.

1. Fill the tank with dechlorinated water matched to your main tank’s temperature. In Singapore, room-temperature tap water (treated with Prime) is usually close enough — check with a thermometer to confirm.
2. Transfer the cycled sponge filter from your main tank. Connect the air pump and ensure the filter is running.
3. Add a hiding spot. A PVC elbow joint, overturned ceramic pot, or dark-coloured plastic cup provides a retreat for the stressed fish.
4. Cover the tank. A glass lid, acrylic sheet, or even cling wrap with air holes will prevent the fish from jumping out.
5. Acclimate the fish. Float the fish in a bag or container for 15-20 minutes to equalise temperature, then gently release it into the hospital tank.
6. Begin treatment according to the medication’s instructions (see below).

Medication Protocol

Always identify the disease or condition as accurately as possible before reaching for medication. Incorrect treatment wastes time and further stresses the fish. For a comprehensive overview of common medications and their uses, see our aquarium medication guide.

General Medication Guidelines

• Follow dosing instructions precisely. More medication does not mean faster recovery — overdosing can be lethal, particularly with copper-based and formalin-based products.
• Remove activated carbon from the filter. Carbon adsorbs medication from the water, rendering it ineffective. Remove any carbon media before dosing. The sponge filter itself is fine.
• Maintain water quality throughout treatment. Test ammonia and nitrite daily if possible. Perform water changes as needed, redosing medication proportionally to the volume replaced.
• Complete the full course. Do not stop medication early because the fish looks better. Pathogens that are suppressed but not eliminated will return, potentially with increased resistance.
• Keep the tank dark. Many medications are light-sensitive (methylene blue, for example, degrades under light). Minimise light exposure during treatment.
• Feed sparingly. Offer small amounts of food once daily. Remove uneaten food promptly to prevent water quality deterioration.

Common Medication Protocols

When to Return Fish to the Main Tank

Returning a fish to the display tank too early risks reintroducing the disease and undoing your treatment. Follow these criteria.

• Symptoms have fully resolved. Not just “looking better” — all visible signs of disease (white spots, fin damage, lesions, bloating) should be absent.
• The full medication course is complete. Even if the fish appears healthy, finish the recommended treatment duration.
• The fish is eating normally. A good appetite is one of the most reliable indicators of recovery.
• Observe for 3-5 additional days. After completing treatment, keep the fish in the hospital tank for a few more days with clean, unmedicated water. Watch for any relapse before returning it to the main tank.
• Acclimate when returning. Drip acclimate or float the fish to match the main tank’s temperature and water chemistry, especially if the hospital tank parameters have drifted during treatment.

Dual Use as a Quarantine Tank

Your hospital tank doubles as a quarantine tank for new fish arrivals. Quarantining new fish for 2-4 weeks before adding them to your display tank is one of the most effective ways to prevent disease introduction. For a detailed quarantine protocol, see our guide to quarantining new fish.

Quarantine vs Hospital: Key Differences

The physical setup is identical — same tank, same sponge filter, same bare-bottom approach. The only difference is the protocol. After using the tank for treatment, thoroughly clean and disinfect it before using it for quarantine (rinse with dilute bleach solution, then rinse exhaustively with dechlorinated water and air-dry).

Frequently Asked Questions

Can I use a plastic container instead of a glass tank?

Yes. A food-grade plastic storage tub works fine as a temporary hospital tank. Ensure it has never contained cleaning chemicals, is large enough (20-40 litres), and is positioned on a stable surface. The only downside is reduced visibility for observation, though clear tubs address this issue.

Do I need to do water changes during medication treatment?

Yes, usually. In an uncycled or partially cycled hospital tank, daily or every-other-day water changes of 20-30% are often necessary to manage ammonia and nitrite. After each water change, redose medication proportionally to the volume of new water added — not the total tank volume. Check your specific medication’s instructions, as some treatments have specific water-change protocols.

How do I sterilise the hospital tank between uses?

After treatment, empty the tank completely. Rinse all equipment (tank, sponge filter, hiding spots) with a dilute bleach solution (1 part household bleach to 10 parts water). Let everything soak for 15-20 minutes, then rinse thoroughly — at least three times — with clean water. Allow everything to air-dry completely before storing. The sponge filter should be returned to your main tank to re-colonise with beneficial bacteria.

My fish is sick but I do not have a hospital tank ready. What do I do?

In an emergency, any clean, watertight container will work — a bucket, plastic tub, or even a large food-storage container. Fill it with dechlorinated water from your main tank (temperature-matched), add an air stone for oxygen, and transfer the sick fish. Perform daily 50% water changes since you will not have a cycled filter. This is not ideal for extended treatment, but it works in a pinch while you source a proper tank.

Be Prepared Before You Need It

The time to set up a hospital tank is before you have a fish emergency, not during one. A basic setup — a 20-30 litre tank, sponge filter, air pump and dechlorinator — costs under $50 SGD and can be stored under a table or in a cupboard when not in use. Keep the sponge filter running in your main tank so it is always cycled and ready to go.

If you need help setting up a hospital tank or diagnosing a fish health issue, visit us at Gensou, 5 Everton Park, Singapore. We stock sponge filters, air pumps, medications and everything else you need for effective fish treatment. With over 20 years of experience, we have seen and treated almost every freshwater fish disease — bring your questions and we will help you get your fish healthy again.

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