Water chemistry is central to aquarium design, and it provides many potential applications for discussion in undergraduate chemistry and engineering courses. Marine aquaria and their life support systems feature many chemical processes. A life support system consists of the entire recirculation system, as well as the habitat tank and all ancillary water treatment processes. Many fundamental concepts learned in general chemistry, for example, unit conversion, solution concentrations, stoichiometry, redox reactions, and acid-base chemistry are all key to understanding the life support system. This article uses a hypothetical tank to house ocean sunfish as a model to show students the calculations and other considerations that are needed when designing a marine aquarium. (Contains 2 figures.)