Every aquarist eventually learns the same lesson the same way: a new fish goes into the display tank, looks fine for 5 days, then spots appear on a tang, then a clown, then 6 corals retract, then half the livestock is dead. The lesson is to never skip quarantine again. A quarantine tank is a 80 to 150 dollar insurance policy that prevents disasters affecting thousands of dollars of livestock. The 30 day protocol below works for freshwater and marine, gives time for parasites to manifest and be treated, and lets new fish establish before joining the display community. This guide covers equipment, the day by day protocol, common treatments, and the reasons aquarists skip QT (and why they regret it).
Why QT exists
New fish from any source (online retailer, local fish store, wild caught, captive bred) potentially carry parasites and pathogens. The most dangerous in saltwater are marine velvet (Amyloodinium ocellatum), marine ich (Cryptocaryon irritans), and brook (Brooklynella hostilis). In freshwater the common threats are freshwater ich (Ichthyophthirius multifiliis), columnaris, and fin rot bacteria. A fish carrying any of these enters the display and seeds the entire tank within 48 to 72 hours.
A QT does three jobs:
- Isolates the fish so disease cannot spread to the display
- Lets the aquarist observe behavior and feeding
- Applies prophylactic medication that would damage corals and invertebrates in the display
The QT also gives the new fish stress free time to eat, gain weight, and recover from shipping.
Equipment list
A working quarantine setup costs 80 to 150 dollars total:
- 10 to 20 gallon glass tank (20 long is preferable for tangs and active fish)
- Submersible heater (50 to 75 watt depending on tank size)
- Sponge filter with air pump and tubing (Hikari Bacto Surge, ATI Hydro Sponge)
- LED light (basic, no need for plant or reef spectrum)
- Air stone and air pump (Tetra Whisper)
- PVC pipe pieces for hiding cover (4 inch length, 1 to 2 inch diameter)
- Plain HDPE or PETG plastic bin lid for cover
Do not add substrate. A bare bottom QT is easier to clean, faster to inspect for parasites, and absorbs copper consistently when treating.
Critical: the sponge filter must be cycled before fish arrive. Run the sponge in the display tank sump for 3 to 4 weeks ahead of time. When QT is needed, move the cycled sponge to the QT and the biological filter is instant. A second permanent sponge stays in the sump for the next QT cycle.
The 30 day observation protocol
Day 0: Acclimate the new fish to QT. Drip acclimate over 60 minutes if water parameters differ significantly. Net out and place in QT (do not pour in store water). Turn lights off for 12 hours.
Days 1 to 3: Lights on, minimal disturbance. Offer food but do not stress with handling. Test ammonia and nitrite daily. A small ammonia bump (under 0.5 ppm) is normal as the cycled sponge adjusts to the new bioload.
Days 4 to 7: Begin observation. Check daily for:
- White spots (ich)
- Velvet (gold dust appearance, rapid breathing)
- Stringy white poop (internal parasites)
- Frayed fins (fin rot)
- Cotton on body (columnaris)
- Heavy mucus or scratching against rocks
Days 8 to 14: Apply prophylactic treatments if running treatment QT (see treatment section below). For observation only QT, continue daily inspection.
Days 15 to 28: Continue observation. Most parasites manifest by day 14. New symptoms after day 21 are rare but possible.
Day 29: Final observation day. The fish should be eating well, behaving normally, and parasite free.
Day 30: Transfer to display. Drip acclimate from QT to display water over 60 to 90 minutes.
Treatment QT (marine fish)
For marine fish, many reefers run treatment QT rather than observation only, because tangs and other fish frequently carry parasites that take longer than 30 days to show symptoms.
Copper treatment for ich and velvet.
- Day 1 to 3: Ramp Cupramine from 0 to 0.5 ppm in 0.1 ppm daily increments (use the included test kit)
- Day 4 to 21: Maintain 0.5 ppm copper
- Day 22: Begin chemi pure or carbon to remove copper
- Day 25: Copper at 0 ppm, fish ready for transfer
Prazipro for flukes and worms.
- Run alongside or after copper treatment
- Day 1: Dose 1 teaspoon per 20 gallons
- Day 7: Second dose
- Day 14: Third dose
- Day 21: Water change to remove residual
Tangs, angels, and butterflies should always go through full copper and prazipro treatment regardless of visible symptoms.
Treatment QT (freshwater fish)
Freshwater requires a different approach because copper is toxic to many freshwater invertebrates and plants that may eventually share the display.
Freshwater ich (heat and salt method).
- Raise temperature to 86 degrees Fahrenheit over 24 hours
- Add 1 tablespoon aquarium salt per 5 gallons (not for catfish or scaleless fish)
- Hold for 10 to 14 days past last visible spot
- Daily 25 percent water changes during treatment
API General Cure (parasites and flukes).
- Dose per package (1 packet per 10 gallons)
- 48 hour treatment, water change, repeat in 5 days
Kanaplex (bacterial fin rot, columnaris).
- 3 day treatment
- Water change
- Repeat if symptoms persist
Common QT mistakes
- Skipping cycling and dumping ammonia on a sick fish (stress kills more fish than disease)
- Adding substrate, which absorbs copper inconsistently and skews dosing
- Using the same net between QT and display (transfers parasites)
- Quarantining multiple fish at once and not isolating shedders
- Cutting the timeline short to 14 or 21 days
- Treating without identifying the disease first
- Mixing medications without checking compatibility (copper plus prazi is fine, copper plus formalin can be toxic)
When QT pays for itself
A 200 dollar tang dying in QT is sad. The same tang carrying ich into a 4000 dollar SPS display and triggering a tank crash costs the tang plus 80 percent of fish and significant coral stress. The QT investment pays for itself the first time it catches one parasite outbreak. Every reefer with a stocked display recommends QT, almost universally because they have all run the alternative experiment.
See our aquarium water parameters explained for the parameters to test in QT, and fish disease ich and fin rot for treatment specifics. The /methodology page documents our protocols.
Frequently asked questions
Do I really need a quarantine tank?+
If you ever want to add new fish without risk to the display tank, yes. A QT setup costs 80 to 150 dollars (10 to 20 gallon tank, sponge filter, heater) and prevents the most common reef tank disaster: a new fish bringing ich, velvet, or brook disease into a stocked display. One velvet outbreak in a stocked tank wipes 80 percent of livestock in 7 to 10 days.
How long should fish stay in quarantine?+
30 days minimum from the day the last fish entered QT. Marine ich has a 28 day life cycle at 78 degree water. Freshwater ich has a 14 to 21 day cycle. The 30 day standard catches both plus most other parasites. Skipping to 14 days saves time on paper but lets dormant parasite cysts hatch in the display tank later.
What is the difference between observation and treatment QT?+
Observation QT is 30 days at proper parameters with no medication, watching for symptoms. Treatment QT applies prophylactic copper (Cupramine at 0.5 ppm for 21 days) and prazipro (1 dose per week for 3 weeks) regardless of symptoms. Treatment QT is recommended for marine fish because parasites often hide as adult fish develop immunity but still carry pathogens.
Can I use the display tank water in the QT?+
Yes for freshwater. For saltwater, use freshly mixed salt water, not display water, because display water carries the parasites you are trying to detect. Match temperature within 1 degree and salinity within 0.001 SG to reduce transfer stress. The QT should be cycled separately using a sponge filter that lives permanently in the display sump.
What if my fish gets sick in quarantine?+
That is exactly why the tank exists. Identify the disease (ich, velvet, brook, flukes, fin rot), apply the matching medication, extend the QT 30 days past the last symptom. The display tank stays safe. Common medications: Cupramine for ich and velvet, prazipro for flukes and worms, kanaplex for bacterial infections, formalin for stubborn parasites.
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