Quarantine tank setup: what you need and how long

Why quarantine at all

Marine ich (Cryptocaryon), velvet (Amyloodinium) and freshwater ich (Ichthyophthirius) all multiply off the fish, in the water and on surfaces, and survivors can carry them without obvious signs. UF/IFAS warns that active freshwater ich can appear 1–3 weeks after shipping at warm temperatures. In a quarantine tank you can watch for that and treat with copper, formalin or salt at full strength. In a reef display you can't: copper kills most invertebrates and is bound by calcium carbonate rock and sand, so the usual cure is off the table. Our white spots on fish page covers the diseases themselves.

Tank size

Bulk Reef Supply's rule of thumb: a 20 gallon, 24 inch long tank is fine for most fish up to 4 inches, and a 40 breeder or similar 36 inch tank is best for larger fish. Its shopping list frames it as a basic 10–40 gallon glass or acrylic tank sized to the number and size of fish you bring in at once. Bigger tanks are more stable, but they also need more medication and bigger water changes.

Equipment

• Heater, sized small. BRS warns that small tanks overheat quickly with an oversized heater. The heater wattage calculator sizes one.
• A filter with cycled media. A hang-on or internal sponge filter, with media that has lived in the display sump or a cycled sponge. Without it, BRS says, ammonia will be a threat and heavy water changes are to be expected. BRS's shopping list does allow running without a biofilter if you commit to frequent large water changes.
• Air pump and air stone. Parasites can make breathing hard, and some medications lower oxygen (BRS).
• PVC pipe for shelter. Short lengths of 2–4 inch PVC give fish somewhere to hide, and BRS notes PVC won't absorb medications the way porous rock and decor can.
• A tight lid or screen top, because stressed fish jump.
• A solid-colour background to calm fish and make spots easier to see, and a simple low-output LED if you want to watch closely.
• Test kits: ammonia, nitrite and nitrate, a thermometer, a refractometer, and a copper test kit if you'll treat with copper. BRS's list keeps quarantine salt at 35 ppt.
• Its own net, siphon and bucket. UF/IFAS says not to share nets, siphons or other equipment between tanks unless they're disinfected.

What not to put in it

• Sand. BRS: the bottom should be bare; sand can harbour the substrate-dwelling stages of parasites and makes siphoning waste harder.
• Live rock or porous decor. It absorbs medications (BRS), and calcium carbonate rock and sand bind copper (UF/IFAS), making the dose unpredictable.
• Corals and invertebrates alongside fish being treated. Copper kills most invertebrates.

How long to quarantine

For marine fish, UF/IFAS advises at least 3–6 weeks at 24–27 °C, longer when ich is suspected, and CORAL Magazine recommends at least 2–4 weeks for every incoming fish, captive-bred included. For freshwater fish, UF/IFAS gives a minimum 30-day quarantine. The clock restarts if you add another fish to the quarantine tank, since the newcomer can bring disease of its own.

Treating in quarantine

For marine ich, the two standard approaches are copper held at 0.15–0.20 mg/L free copper for 3–6 weeks and tested at least twice a day (UF/IFAS), or the tank-transfer method: moving fish to a clean, dry tank every three days so the parasite's free stages are left behind (Bulk Reef Supply). Velvet needs copper for at least 10–14 days, and BRS doesn't recommend tank transfer for it. BRS's shopping list names one medication per problem (copper for ich and velvet, nitrofurazone for bacterial infections, formalin or an aldehyde product for Brooklynella and Uronema, praziquantel for flukes) and says to use only one at a time.

For freshwater ich, UF/IFAS uses salt at 4–5 g/L for 7–10 days at 75–79 °F, or formalin at 25 mg/L, and says never to stop until deaths have stopped; the aquarium salt calculator works out the grams. Whatever you use, follow the label and test daily for ammonia: medications, especially antibiotics, can knock back a filter's bacteria.

Habits that keep it working

• Keep it running. A filter sponge kept in the display sump means a seeded filter is ready the day a fish arrives.
• Feed and watch. Quarantine is where you confirm a fish is eating, which matters as much as disease for picky species such as the mandarin dragonet.
• Change water from the display's salt mix at the same salinity, so the move to the display is easy.
• Break it down and dry it between batches if a disease ran through it.

Corals and frags get a different treatment: a dip and inspection for pests. See the coral dip guide.