Lastly put the lid on the tank and let it cycle for one to two days before adding any fish to the tank. Watch the tank for cloudiness and check the temperature and P.H. of the water. If all is clear you may add a few hardy fish. It is important to choose fish that can withstand high levels of nitrites and ammonia, because these levels are always high in a new tank due to the nitrogen cycle. A general rule is to wait another thirty days before adding additional fish, because that is the incubation period for most fish illnesses. In addition, test the nitrite and ammonia levels before adding these additional fish. The ammonia levels should return to zero. This also takes about a month. There are a few basic tips that will keep fish healthy. Last on the list for keeping fish healthy, is to keep them happy. Try to recreate their natural environment. It is recommended to keep a variety of plants in the aquarium for guppies to seek refuge. There should be about one to two inches of substrate in the bottom of the tank. Colored rock or dead crushed coral make a nice addition to the aquarium, and may help to make the fish feel more at home. A few examples of tropical invertebrates are tubeworms, red hermit crabs, cleaner shrimp and the sea apple. All of this marine life is compatible in terms of water conditions. They require a water temperature between seventy five and seventy nine degrees Fahrenheit, a P.H. between 8.2 and 8.4 and a salinity content of 1.020-1.024. Sand sharks are usually smaller in size than other sharks and move fairly slowly. These sharks are found all over the Atlantic Ocean, and are the most common type of shark. Although these sharks would seem to be the perfect aquarium kept fish, because of their smaller size, they are not. They still grow to reach an average length of about five feet, and can weigh as much as three hundred pounds. By doing this, you will eliminate the chances algae utilizing the nutrients added and the extra lighting. Quick growing plants are recommended as well as some floating plants. Certain types of fish, such as a catfish, like to seek cover from direct light. The floating plants will provide this escape for the fish and will add a pleasing effect to the design and decoration of the aquarium.