Aquarium temperature: the right range for your fish

Beginner guide · About 5 minutes to read · By Andy · Updated Oct 26, 2026

Fish can't warm themselves up or cool themselves down, so the water temperature controls how fast they eat, grow and fight off disease. Here's the right temperature for common fish, how to keep it steady, and what to do if your tank gets too hot or too cold.

The quick answer

Tropical fish (most community fish): 75–80°F (24–27°C). 76–78°F suits most mixed tanks.
Bettas: 78–80°F (26–27°C).
Goldfish and other coldwater fish: 65–72°F (18–22°C).
Whatever the number, keep it steady. Swings of more than about 2°F in a day stress fish more than being a degree or two off.

Temperature chart by fish

The ranges used by the free stocking calculator, which also finds the range that suits every fish in your tank:

Fish	°F	°C
Betta (male)	76–82°F	24–28°C
Neon tetra	72–80°F	22–27°C
Cardinal tetra	75–82°F	24–28°C
Ember tetra	73–82°F	23–28°C
Harlequin rasbora	72–80°F	22–27°C
Zebra danio	65–77°F	18–25°C
White cloud mountain minnow	60–72°F	16–22°C
Guppy	72–80°F	22–27°C
Platy	70–80°F	21–27°C
Molly	72–80°F	22–27°C
Swordtail	72–79°F	22–26°C
Dwarf gourami	75–80°F	24–27°C
Honey gourami	72–82°F	22–28°C
Pearl gourami	77–82°F	25–28°C
Corydoras (bronze or peppered)	70–78°F	21–26°C
Pygmy corydoras	72–79°F	22–26°C
Kuhli loach	75–86°F	24–30°C
Otocinclus	72–79°F	22–26°C
Bristlenose pleco	72–80°F	22–27°C
Angelfish	76–84°F	24–29°C
Fancy goldfish	65–72°F	18–22°C
Cherry shrimp	65–80°F	18–27°C
Nerite snail	72–78°F	22–26°C
Mystery snail	68–82°F	20–28°C

Do I need a heater?

For tropical fish, yes, unless your room never drops below about 75°F, day or night, all year. Most homes are cooler at night and in winter. A heater with a thermostat keeps the water steady. Find the right size with the heater calculator and see the best aquarium heaters. Goldfish and white clouds usually don't need one.

Tank too cold?

Signs: fish are sluggish, hide near the bottom, eat less, and get sick more easily, including ich.
Check the heater is plugged in, its light comes on, and it's set correctly. Heater dials are often a few degrees off, so trust the thermometer.
Check the size. A heater that's too small can't keep up on cold nights.
Warm it slowly, no more than about 2°F a day.

Tank too hot?

Signs: fish gasp at the surface, because warm water holds less oxygen. See fish gasping at the surface.
Unplug the heater if it's stuck on, and replace it.
Add surface movement with an air stone or by lowering the water level a little under the filter outflow.
Lift the lid, turn the light off, and point a fan across the water. Evaporation cools it a few degrees.
Cool it slowly. Float a sealed bag of ice or a frozen water bottle, never dump ice in, and aim for no more than 2 to 3°F an hour.
Keep the tank out of direct sun.

Tips for a steady temperature

Use a thermometer on the side away from the heater, and glance at it every day.
Match the temperature of new water during water changes, within a degree or two.
Keep a lid on. It holds heat in and cuts evaporation.
For big tanks, two heaters at opposite ends heat evenly and give you a backup if one fails.

Temperature picks

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