Change about a third of the water in the aquarium at a time, because this type of change will cause the least amount of disturbance to the fish and other inhabitants. This will need to be done every two to three weeks. Use either a bucket or a siphon to remove the water from the tank. Try to remove any loose or floating debris at this time. Sand sharks can be kept in a tank with other large fish. The sharks are usually fed three to four times a week to discourage them from eating tank mates. For the most part this works well, although, every so often some of the fish seem to disappear. When housing sharks, care should be taken to ensure there is adequate space for swimming. The most distinguishing feature of a catfish is the prominent "barbells", which look like whiskers on a cat, hence giving these one of a kind fish their name. The other thing that set catfish apart from any other fish is the fact that they have no scales. They also possess a strong, hollow ray on their fins that a stinging protein can be emitted from if the fish is irritated or in danger. 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. Once the gravel has been cleaned, place it aside. You will not be putting it back in the tank at this time. Step 4 (Cleaning the tank) Now it's time to clean the inside of the tank. This can be a tedious chore if there is a lot of build-up on the glass. Some freshwater aquariums have algae growth on the glass. Add chemicals and chlorine weekly so the balance within the tank remains the same. At this time, it is best to test the water for the ammonia and nitrate levels. Don't overlook testing the pH of the water as well. If you are raising live plants, tend to them each week. Trim them back if they are getting too big, and remove any dead or sick leaves.