Remember the unexplained algae blooms that started taking over your reef and smothering your corals and live rock? Corals and inverts that had been perfect all of a sudden starting to die off and your fish getting sick? The oxygen retention level of the water is directly related to temperature. Once the summer heat kicked in, the oxygen level dropped and you started loosing livestock. This does not start happening at an extremely high temperature, it starts happening at a mere 80 degrees. The money you lost would have purchased the chiller that would have kept all this from happening. Never mind all the work.