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A 20-gallon aquarium is generally considered the practical minimum for a single firefish, making them one of the most accessible marine fish for smaller reef setups. Unlike mandarin dragonets, where tank size is primarily about copepod population, firefish tank size is more straightforward - they need enough space to hover comfortably in the water column, adequate rockwork with bolt holes, and stable water quality. Bigger tanks are always better, but firefish are genuinely manageable in smaller systems.
Firefish Tank Size at a Glance
| Practical minimum | 20 gallons |
| Recommended for community reef | 30-50 gallons |
| Key setup requirement | Tight-fitting lid and bolt holes in the rockwork |
| Refugium required? | No - but beneficial |
Can a Firefish Live in a 20-Gallon Tank?
Yes - a 20-gallon tank is a workable setup for a single firefish. Firefish are small fish (3 inches adult size) that hover in the mid-water column and do not require large swimming territories. A 20-gallon nano reef can comfortably house a clownfish pair and a single firefish, provided filtration, maintenance, and compatibility are appropriate. Firefish appreciate open swimming space in front of the rockwork rather than densely filling the entire aquarium with rock. In a 20-gallon tank:
- Keep only one firefish - two firefish in a 20-gallon will often fight
- Choose peaceful tankmates that do not compete for territory or harass the firefish
- A tight-fitting lid is essential - jumping risk is the same regardless of tank size
- Provide adequate bolt holes in the rockwork throughout the tank
- Maintain stable water quality - smaller water volumes fluctuate more quickly
See our Best Saltwater Aquarium Tanks guide.
Recommended Tank Size: 30-50 Gallons for a Community Reef
A 30-50 gallon tank gives a firefish more comfortable conditions and more flexibility for tankmates. In a larger tank:
- Water parameters are more stable and forgiving
- More rockwork can be provided, giving the firefish more bolt hole options
- A wider range of peaceful tankmates can be added
- A refugium can be incorporated more easily, which benefits the overall system
A 30-gallon tank comfortably houses a firefish alongside a clownfish pair and a royal gramma, which is one of the most popular beginner reef combinations. See our Clownfish Care Guide and Royal Gramma Care Guide.
What Matters More Than Tank Size
A Tight-Fitting Lid
Tank size has no bearing on jumping risk. A firefish in a 100-gallon tank with an open top is at just as much risk as one in a 20-gallon tank. A tight-fitting lid or fine mesh screen cover is the single most important piece of equipment for a firefish tank, regardless of size. See our Firefish Jumping guide.
Bolt Holes in the Rockwork
Firefish need bolt holes - small caves or crevices in the rockwork they can instantly retreat into when startled. A firefish without adequate bolt holes will be chronically stressed regardless of tank size. Ensure the aquascape provides multiple bolt holes distributed throughout the tank. See our Best Live Rock and Reef Rock guide.
Stable Water Quality
Firefish require a fully cycled tank with ammonia and nitrite at 0 ppm. Most reef keepers aim to keep nitrate below about 20 ppm while maintaining zero ammonia and nitrite. Smaller tanks require more frequent testing and water changes to maintain stable parameters. Test weekly. See our Best Reef Test Kits guide.
Peaceful Tankmates
A firefish in a large tank with aggressive tankmates will be more stressed than a firefish in a small tank with peaceful companions. Tankmate selection matters more than tank size for firefish wellbeing. See our Firefish Tankmates guide.