Free fish health planning tool

Free Fish Quarantine Tank Size Calculator

A fish quarantine tank size planner estimates how large a temporary isolation tank should be for new or sick fish, based on how many fish you have and how big the largest one grows. It also builds a freshwater or saltwater setup checklist and a day-by-day quarantine timeline.

Tank size rangeFreshwater & saltwaterSetup checklistQuarantine timeline
Planning guidance, not veterinary diagnosis. Dose any medication only as the product label directs and with guidance from an aquatic veterinarian. Ammonia control, aeration, stable temperature, daily observation, and species-specific requirements matter more than any size estimate. The suggested volume is for temporary quarantine only and is not permanent stocking advice.

Quarantine inputs

Describe the fish you are quarantining

Aquarium type

Use expected adult size, not current size.

Suggested temporary quarantine tank

20–29 gallons

about 76–110 liters · start with a 20 gal long tank; a 29 gal tank gives more stability.

Min. tank length
12 in
Planning volume
~15 gal
Quarantine
42 days

This is a temporary quarantine volume, not a permanent stocking recommendation. Check species-specific adult size and display-tank needs separately.

What increases the space you need

  • Saltwater holds less dissolved oxygen, and many marine fish arrive stressed from collection and shipping, so the plan allows more water per inch of fish.
  • Several fish of similar size add close to a full body length of space each.

Quarantine timeline

  1. Days −14 to −1

    Prepare and seed

    Set up the tank, seed the filter in an established system, and confirm heater, aeration, and stable readings for several days.

  2. Day 0

    Arrival and acclimation

    Acclimate gently, keep lights dim, record the fish's condition, and avoid feeding heavily on the first day.

  3. Days 1 to 7

    Settle and test daily

    Test ammonia and nitrite daily, offer small meals, and note breathing, appetite, and any visible signs of disease.

  4. Days 8 to 28

    Observe or treat per plan

    If you use a preventive treatment, follow the label schedule exactly and test water more often; otherwise continue careful observation.

  5. Days 29 to 42

    Final symptom-free observation

    Finish without medication. Any new symptoms restart this phase instead of moving fish to the display.

  6. Day 43

    Transfer and clean up

    Move healthy fish without quarantine water, then break down, disinfect, rinse, and dry the quarantine equipment.

Saltwater setup checklist

Equipment

  • 20 gal long tank (or larger) with a tight lid; bare bottom makes cleaning and observation easier.
  • Adjustable heater with a guard, plus a separate thermometer to verify it.
  • Air pump with an air stone for strong surface agitation and oxygen, especially during treatment.
  • Sponge filter or media pre-seeded in an established, healthy tank for at least two weeks.
  • Hiding places such as PVC fittings or plastic caves that can be cleaned or discarded.
  • Dedicated nets, buckets, siphon, and gloves that never touch the display tank.
  • Refractometer or calibrated salinity meter and a supply of pre-mixed saltwater.

Water quality and testing

  • Ammonia and nitrite test kits (daily in the first week, then every one to two days).
  • Match temperature, salinity, and pH to the source water before fish arrive.
  • Water change schedule ready: small, frequent changes with temperature-matched water.

Husbandry and records

  • Daily observation log: appetite, breathing rate, fins, skin, spots, and behavior.
  • Feed lightly and remove uneaten food to limit ammonia spikes.
  • Work on the quarantine tank last each day and wash hands between systems.
  • Medication plan confirmed with the product label and, ideally, an aquatic veterinarian before dosing.
  • Remove chemical filtration such as carbon during treatment unless the label says otherwise.
  • Keep live rock, sand, corals, and invertebrates out of a treatment tank; many medications harm them or bind to calcium carbonate.
Log quarantine water tests, livestock, and observation notes in My Reef Log.Start tracking free

How the size estimate works

The planner adds up an effective length of fish from the largest adult length and how the rest of the group compares, then applies more water per inch for saltwater fish, heavy bioloads, and aggressive temperaments. It also sets a minimum tank length of four to six times the largest fish so it can turn and swim, and rounds up to common tank sizes.

Why it gives a range

Body shape, activity, and husbandry vary too much for one exact number. The smaller size is a practical starting point; the larger size adds stability and dilutes waste between water changes.

Quarantine is temporary

A quarantine tank holds fish for a few weeks under close watch with frequent testing and water changes. That makes it different from a display tank, which must support each species' adult size, swimming space, and social needs for years.

Freshwater and saltwater differences

Saltwater fish get more water per inch and a longer default timeline because marine fish are often wild-collected and some parasites have slow life cycles. Freshwater setups need dechlorinated water matched to the species' pH and hardness.

How to use the quarantine tank planner

  1. Step 1

    Describe the fish

    Choose freshwater or saltwater, then enter fish count, the largest expected adult length, size mix, bioload, and temperament.

  2. Step 2

    Set the purpose and length

    Pick observation, planned preventive treatment, or active treatment, and set the number of quarantine days.

  3. Step 3

    Review the tank range

    Read the suggested tank-size range, minimum tank length, and the factors that increase the space you need.

  4. Step 4

    Follow the checklist and timeline

    Prepare the equipment, seed the filter, then follow the day-by-day phases and copy the plan summary for your records.

Fish quarantine tank FAQ

What size quarantine tank do I need?

Many hobbyists use a 10 to 20 gallon tank for one or two small fish and 29 to 55 gallons for larger or more active fish. Size it from the largest adult length, the number of fish, and bioload, and keep the tank long enough for the biggest fish to turn easily.

How long should fish stay in quarantine?

Veterinary references commonly suggest at least 30 to 60 days for valuable fish. Plan longer when a treatment is used, and restart the symptom-free observation period if new signs of disease appear.

Is quarantine tank size the same as permanent stocking?

No. A quarantine tank is a temporary, closely managed holding system with extra testing and water changes. Choose the display tank from each species' adult size, behavior, and long-term needs, not from this estimate.

What equipment does a fish quarantine tank need?

Use a lidded bare-bottom tank, a guarded heater and thermometer, strong aeration, a pre-seeded sponge filter, easy-to-clean hiding places, an ammonia test kit, and nets or buckets used only for quarantine. Saltwater setups also need accurate salinity measurement.

Can this tool tell me which medication to use?

No. It is planning guidance, not a veterinary diagnosis. Follow the product label for any medication and ask an aquatic veterinarian to diagnose disease and confirm treatment and dosing for your species.

References

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