Mineral studies in fish must account for contributions both from the diet and the water, and the latter can be a significant source of minerals (Davis and Gatlin, 1996). Hard water contains higher concentrations of calcium, magnesium or both than soft water, and fish raised in hard water may need fewer minerals in the diet than those raised in soft water (Lall, 2002). Furthermore, agastric specieslike fathead minnow may be more dependent on dietary minerals when raised in soft water, because they do not secrete hydrochloric acid during digestion and may absorb dietary minerals less efficiently.