Aquarium Moss is seen most often floating in the tank. They do not need to be held down by a large rock although it is an option. They can be placed in a tank of water and left alone. They can be put with water with aquatic life or without. More homeowners are creating aquariums with just plants because they need the little cleaning and little maintenance. Most aquatic plants can create their nutrients in the water that it aids in getting rid of algae and keeping it down to a minimum.