Natural reefs spread out no more than thirty degrees north or south of the equator. In this area water temperatures are very stable between 25 and 27 degrees celcius, this is the range we should aim for in our aquariums.
Corals are adapted to thrive with a very small temperature range, therefore a difference of one or two degrees could have a serious detrimental effect. During the summer months a reef aquarium can reach temperatures exceeding 29 degrees celcius stressing the importance of installing an aquarium cooler.
Aquarium coolers can be very expensive but if you compare the cost of a cooler to the cost of loosing all your livestock then you will see it is definately worth the investment.