How to Quarantine New Fish Complete Guide: Protocol and Duration

The hobbyists who never experience a tank-wide disease outbreak share one habit: they quarantine every new fish, every time, without exception. This how to quarantine new fish complete guide from Gensou Aquascaping at 5 Everton Park details the full protocol — QT tank specification, stocking rules, duration, observation checkpoints, and prophylactic treatment decisions — calibrated for SG conditions where tropical heat and mixed-source retailers raise pathogen risk. Quarantine adds three to four weeks to every fish purchase and saves years of heartbreak.

QT Tank Minimum Specification

30-40 L is the standard size. Bare glass bottom simplifies observation, medication and cleaning. A cycled sponge filter — ideally one that has been running in your display tank for 30+ days — provides instant biological filtration. Heater set to 26-27°C, simple air stone, covered top, dim lighting. Two or three plastic hides or a piece of PVC pipe offer cover. Total cost: $80-130 from C328 Clementi or Serangoon North specialists. Keep it stored dry and ready to assemble in 30 minutes when needed.

Dedicated Equipment Only

Nets, siphons, buckets and algae scrubbers used on the QT must never touch the display tank and vice versa. Colour-code them with electrical tape to prevent mistakes. Cross-contamination through shared equipment causes more secondary outbreaks than most hobbyists realise. A dedicated small bucket ($4 at Daiso) and a dedicated net ($5) makes hygiene automatic.

Duration: 21 to 28 Days Standard

The incubation window for most common diseases — ich, velvet, flukes, bacterial infections — runs 7-14 days. A 21-day minimum quarantine catches these; 28 days provides margin for slow-onset internal parasites. Wild-caught species deserve 30+ days. Captive-bred fish from known specialist breeders sometimes justify 14-day abbreviated quarantine. Restart the clock if any symptom appears during QT — treat, clear, then hold the full duration from treatment end.

Stocking the QT

Never mix species from different sources in one QT batch. A single batch from one retailer on one day can share a QT; adding a new batch restarts the quarantine for everyone. Keep stocking light — one or two fish per 10 litres for the QT period — to reduce bioload on the smaller filter. Overcrowded QT tanks spike ammonia, add stress and defeat the entire purpose.

Week One: Observation Only

First seven days, observe without medicating. Feed normally. Test ammonia and nitrite daily; dose Prime and do 20 per cent water changes as needed. Record weight and behaviour: schooling, feeding response, colour, swimming pattern, faeces appearance. Fish arriving stressed may show clamped fins or faded colour for 3-5 days — this alone is not illness. Track a baseline so real symptoms stand out against normal settling behaviour.

Week Two: Prophylaxis Decision

Healthy fish at day 14: decide on preventative treatment. For wild-caught or mixed-source retail fish, a praziquantel course (API General Cure $28) treats flukes and internal parasites over 7 days. Follow with a metronidazole round if hexamita-prone species (cichlids, large angels, discus). For captive-bred from specialist breeders, skip prophylaxis and continue observation. Medicating without symptoms stresses healthy fish — the decision depends on source risk.

Symptom-Driven Treatment

Any symptom during QT is a gift — you caught it before it reached the display. White spots: salt 0.1 per cent plus heat to 30°C for 14 days, or proprietary ich medication. Flashing without spots: praziquantel for flukes. Cotton patches: fungal treatment. Cloudy eyes, pop-eye: bacterial medication. Complete the full treatment course even if symptoms clear early; truncated treatment breeds resistant pathogens. Run the QT clock from treatment completion.

Water Management in QT

Smaller tanks fluctuate faster. Test daily, not twice weekly. 20 per cent water changes every 3-4 days maintain clean conditions without disrupting the cycled sponge. Temperature at 26-27°C unless treating ich at 30°C. pH matching display — do not acclimate a fish to QT parameters only to shock it again on transfer. If your display runs at pH 7.2, match the QT at 7.2 from day one.

Transfer to Display

Day 21-28 with no symptoms: transfer. Drip-acclimate over 30-45 minutes from QT to display even though both are your tanks. Release with display lights dim. Feed lightly as distraction. Monitor display for the next 7-10 days for any late-onset symptoms — rare but possible. Break down QT, clean with hot water (no detergents), dry fully, store for next use. The cycled sponge goes back into the display tank to maintain biological activity until next needed.

Common Quarantine Mistakes

Cutting duration short because the fish “look fine” — the fish that looks fine on day 10 can outbreak on day 15. Adding QT fish to the display “just for a day” to test tank mate compatibility — defeats the quarantine entirely. Treating a healthy QT prophylactically with a cocktail of medications — hurts fish more than it protects. Using display tank equipment in the QT — introduces contamination backwards. Skipping QT because “the shop looked clean” — every wholesaler in SG receives mixed shipments, and even reputable retail tanks carry pathogens.

Building the Habit

Quarantine becomes automatic once you run two or three successful cycles. The QT tank sits ready in a corner; the process takes 15 minutes of daily attention; outcomes are dramatically better. Gensou clients who adopt disciplined quarantine rarely experience full tank crashes, and when issues appear they are contained to the QT rather than the $2000 display. This how to quarantine new fish complete guide represents the difference between hobby fishkeeping and serious fishkeeping — and the price of entry is a small spare tank and four weeks of patience.

Related Reading

• How to Introduce New Fish to Tank Guide
• Hospital Tank Setup Guide
• How to Tell if Fish is Sick Guide
• Ich Treatment Singapore Guide
• Fish Disease Prevention Guide