the use of a special section of the tank or separate tank altogether, called a "refugium." A refugium is, as its name suggests, a sheltered area that shares water with the primary, or display, tank. Refugiums usually contain a deep sand bed to allow anoxic zones to develop within them where anaerobic bacteria can convert nitrate into nitrogen gas, a useful means of nitrate removal. Various types of macroalgae can be grown and harvested from the refugium as another means of nitrate export. As refugiums become more common in marine aquaria, nitrate levels are easily manageable for even the novice hobbyist. Ammonia and nitrite should be tested regularly; any detectable levels (i.e., over 0 ppm) can be indicative of a problem. Nitrates should not exceed 2 ppm in reef tanks, or 20 ppm in fish-only tanks. It is sometimes acceptable to have a small amount of nitrate buildup, as some livestock, especially fish, are fairly tolerant of nitrate. Most corals, while able to assimilate nitrate, cannot be expected to survive, much less thrive, with high nitrate concentrations. Other suggested tests include those for calcium, carbonate alkalinity, magnesium, and other trace elements. It is often beneficial (and necessary) for the aquarist to research the water chemistry parameters for the specific organism that is desired. Acclimation Acclimation is a process that is performed when adding new marine life to an aquarium, particularly for invertebrates, who lack osmoregulation. This process slowly introduces the organisms to the water composition of the new environment, preventing shock resulting from sudden changes in water chemistry. There are several different methods of doing this, including the use of a drip line, or of a measuring cup or other device to slowly mix water from the aquarium tank into a container with the new animal. The drip line or trickle acclimating method is a safe and gentle way to introduce saltwater fish into a new home, and is a fairly simple one to perform. This procedure can be used to acclimate all types of marine as well as freshwater livestock. First, the fish is placed with all the bag water in a bucket or container of sufficient size for the fish to be reasonably covered with the water, and the bucket is then set on the floor next to the aquarium. Using some plastic air line tubing and an air gang valve, a siphon drip line is set up