Fish Tank Aquarium Heaters & ChillersCheck out our wide selection of aquarium heaters and chillers to keep your fish tank at the perfect temperature all year! Fish tank temperature has a direct effect on your fish's metabolism. Lower temperatures can slow down fish's metabolism while can make them sleepy and sluggish. On the other hand, warm water can cause the metabolism to speed up. It is crucial to keep your aquarium temperature within a certain temperature range to keep your fish healthy and happy.