The correct water temperature is essential for the health of ornamental fish and the development of aquatic plants in the aquarium. The water temperature should be kept as close to natural conditions as possible. As in nature, the aquarium can be slightly cooler at night than during the day. In summer, an aquarium can heat up very quickly. This can be problematic and cooling must be provided. A quick remedy is to change the water with cooler water. An aquarium fan can permanently lower the water temperature by 3-4°C through the effect of evaporative cooling. A cooling unit will automatically keep the water temperature within the optimum range.