Hold a tropical community tank at 24 to 26°C and check it with a thermometer at the opposite end from the heater. Species differ, from about 21°C for neon tetras to 28 to 30°C for discus, so match the temperature to every fish you keep. Warm water holds less oxygen, so watch the tank in a heatwave.
What temperature should a tropical fish tank be? For most community fish it’s 24 to 26°C, the range RSPCA Australia gives for tropical fish. Some species want it cooler or warmer, so the right number depends on what you keep. Choose one temperature that suits every fish in the tank, hold it steady with a heater and a thermometer, and watch it in summer.
Scope: the ranges below suit a heated freshwater tank. A species that isn’t listed can differ, so check its own care sheet, and keep only fish that share an overlapping range. Keeping some ornamental species is restricted or banned in parts of Australia. The rules differ by state and change over time, so check your state Fisheries or Biosecurity department before you buy any of the fish named here.
What Temperature Should a Tropical Fish Tank Be? The Short Answer
Tropical fish come from warm waters, so they need a heated tank. RSPCA Australia says to hold a tropical tank at 24 to 26°C using a submersible heater, because normal room temperature is generally too cold and can also fluctuate, which stresses fish.
| Fish or tank type | Typical range (°C) | Note |
|---|---|---|
| General tropical community tank | 24 to 26 | RSPCA Australia guide |
| Neon tetra | 21 to 25 | Cooler than most tropicals |
| Bronze corydoras | 21 to 27 | Wide range, suits many tanks |
| Siamese fighting fish (betta) | 24 to 26 | RSPCA guide; wild-fish records span a wider 22 to 30 |
| Discus | about 28 to 30 | Warmer than most community fish |
The mismatch is the trap. A neon tetra and a discus can’t share a tank, because 24 to 26°C is too cool for one and too warm for the other. Pick fish whose ranges overlap, and set the tank in the middle of the overlap.
Set the Temperature and Keep It Steady
- Size the heater to the water. Aqua One’s manual says 1 watt heats 1 litre, so work out your real litres first. A cold room needs more.
- Place it well. Put the heater near the filter outlet and away from the gravel, and the thermometer at the opposite end of the tank, as the same manual says. A small gap between the heater’s dial and the thermometer is normal.
- Mind the mains. Let a new heater sit in the water for 10 to 15 minutes before switching on. When you do a water change, unplug it first, and never run it out of water.
New to all this? The setup guide shows where the heater fits in the build.
What Temperature Should a Tropical Fish Tank Be in an Australian Summer?
Most tropical-tank advice is written for cooler climates and assumes you only ever heat. In a hot Australian summer, or in northern Australia, a tank in a warm room can overshoot your fish’s range with the heater off. A fan or chiller may then matter more than the heater. Read the thermometer on the hottest afternoon, not just in the morning.
Heat is a double problem. According to the University of Florida IFAS, warm water holds much less oxygen, and fish burn more of it at higher temperatures. Its example: water at 32°C holds about 7.4 mg/L of oxygen at saturation, against about 11.9 mg/L at 7°C.
If the tank climbs above your species’ range:
- Get it out of the sun. RSPCA NSW says to keep tanks away from direct sunlight and windows.
- Turn the heater down or off, and take the lid off or lift it a little so heat can escape.
- Move the surface. Add an air stone or point the filter outlet at the surface, and blow a fan across the water to cool it by evaporation. Keep plugs and cords well away from water.
- Shorten the light period. RSPCA Australia’s maximum is 10 hours a day, and a shorter one adds less heat.
Avoid quick swings. RSPCA Australia flags temperature fluctuation as stressful, so cool the tank steadily rather than dumping in cold water.
Frequently Asked Questions
What temperature should a freshwater fish tank be?
It depends on the fish. A tropical freshwater tank sits at 24 to 26°C according to RSPCA Australia, while some species prefer cooler or warmer water. Always check the range for every species you keep.
Is 28°C too hot for a fish tank?
Yes for most community fish, which top out around 25 to 27°C, but fine for warm-water species such as discus. Check your species, and remember warm water holds less oxygen.
Can I keep tropical fish without a heater?
Not reliably. RSPCA Australia says normal room temperature is generally too cold and fluctuates, so a submersible heater is needed. In a warm climate the tank may still overheat in summer.
What temperature should a betta tank be?
RSPCA Australia gives 24 to 26°C for Siamese fighting fish, kept with a submersible heater. See the Betta Fish guides for more.
How do I check the water temperature in a fish tank?
Use an aquarium thermometer placed at the opposite end from the heater, and read it daily. Compare it with the heater’s dial. A small difference is normal, but a big one means one of them is off.
