I personally run Kent Carbon 24/7, and I change it bi-monthly. Another good brand that I've heard is Black Diamond by Marineland I believe. Some people believe in using carbon and use it religously, and some people feel it is unnecessary. I find that it does remove the oder and will probably take out some of the chemicals that corals release as their defense mechanism.
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32"x32"x20" Cube-ish tank
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