Most tropical aquarium fish are happiest at 24-27°C; goldfish and coldwater fish prefer it cooler at 18-23°C. A thermostat-controlled heater keeps it steady - and stability matters more than the exact number. Here's the right temperature for common fish and how to choose a heater.
Ideal temperature by fish
- Tropical community (tetras, guppies, mollies): 24-27°C.
- Betta: 25-28°C.
- Goldfish / coldwater: 18-23°C.
- Discus: warmer, 28-30°C.
Avoid big swings - a stable temperature beats a "perfect" one that fluctuates. See our care guides for betta, goldfish and guppy.
How to choose a heater
Size the heater to your tank - roughly 1 watt per litre as a starting point. A submersible like the Fluval M-Series suits most tanks; the Fluval E-Series adds a digital display and safety alerts. For larger tanks, step up to the M200 or M300.
In hot weather
Indian summers can push tanks above the safe range - the heater switches off, but you may also need to actively cool the water. See how to keep your aquarium cool.
Frequently asked questions
What temperature should my aquarium be?
Tropical fish: 24-27°C; betta 25-28°C; goldfish and coldwater fish 18-23°C; discus 28-30°C.
What size heater do I need?
Roughly 1 watt per litre as a starting point; colder rooms and larger tanks need a bit more.
Do goldfish need a heater?
Not usually - they're coldwater fish and do fine at stable room temperature, unless your room gets very cold.
Is a stable temperature important?
Very - sudden swings stress fish and weaken their immune system more than a slightly off but steady temperature.
Where should I place the heater?
Near good flow (e.g. by the filter outlet) so heat spreads evenly; fully submerge to the marked line.
What if my tank gets too hot in summer?
Increase surface aeration, use a fan across the surface, and see our summer cooling guide.
Keep temperatures steady with Fluval heaters from Fish Bazaar, delivered across India.
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