Most tropical marine aquariums are kept between 24°C and 26°C, with around 25°C being a common target for reef tanks.

Fish, corals and invertebrates can tolerate some natural variation, but sudden temperature changes are best avoided. Consistency is generally more important than maintaining an exact temperature down to the decimal point.

During summer, aquarium temperatures can rise due to warm room temperatures, lighting and equipment. Cooling fans or aquarium chillers can help prevent overheating, while a reliable heater maintains temperature during colder months.

Aquarium heater requirements depend on the volume of water, room temperature and how much warmer you need the aquarium to be.

For a typical indoor aquarium, a rough starting guide is:

• 50 litres: 50–100W
• 100 litres: 100–150W
• 200 litres: 150–250W
• 300 litres: 200–300W
• 500 litres: 300–500W

These figures assume a reasonably warm room. Aquariums in colder environments may require additional heating capacity.

For larger aquariums, using two smaller heaters rather than one large heater can help distribute heat and provide some redundancy if one fails. A separate temperature controller can offer additional protection against overheating.

Both aquarium chillers and cooling fans can help prevent your aquarium from overheating, but they work in different ways.

Cooling fans blow air across the water's surface, increasing evaporation and removing heat. They're relatively inexpensive to run and can be very effective for smaller temperature reductions. However, increased evaporation means your aquarium will need more freshwater top-ups.

Aquarium chillers actively cool water as it passes through the unit. They're generally more suitable for larger aquariums, consistently warm rooms or systems that need precise temperature control.

For occasional warm days, cooling fans may be sufficient. If your aquarium regularly exceeds its target temperature, particularly during prolonged summer heat, a properly sized chiller may be a more reliable solution.