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Depending on where you live and and whether you have good air conditioning, you may not need a chiller. I live in Texas and keep the house temperature around 71degrees. I can keep my tank at around 72 degrees by using a fan on the sump and not running the skimmer all the time. So I really haven't needed a cooler, but some of our other bimac keepers have.
I also live in Texas, the warmer part, and I have been successful using fans over the sump to get my water temp down to 74 degrees from 78. My apartment is at about 74 degrees. Thanks Nancy for the suggestion! Target has small fans with clips on clearance for about 5 dollars, and we have 3 of them blowing across our sump. Muuuuch cheaper than a chiller. Now I just need an automatic top off, so I can keep up with the evaporation.