When cleaning the tank, you will need remove of stir the gravel to remove sediment that could possibly change the chemical make up of the tank. Use caution when cleaning an acrylic tank and be sure that the cleaning supplies being used will not harm the tank in any way. The best thing to use to remove algae is phosphate drops. 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. Sharks by nature cruise the open waters. Home aquariums were generally kept only in coastal towns where the fish were readily accessible. Today, however many things of changed. We wouldn't dream of dipping a net into an aquarium and frying up the family pet for dinner. That's what Red Lobster is for. Home aquariums are for our personal entertainment and enjoyment. Just like any living creature, a fish's body requires water in order to function properly. Water is absorbed through a fish's skin in the freshwater environment. Alternatively, a saltwater fish actually has to drink the salt water, because the body fluids are extracted through the skin by osmosis. The salt is then excreted in the form of highly concentrated urine. Debris in the tank from fish excretions help to generate the good bacteria that is needed in order for the fish to survive. Since there are currently no fish in the tank this will take some time. It usually takes about four to six weeks. Once you have purchased your fish, let them float on the surface of the tank in the bag for about fifteen minutes. Stay away from under gravel filters because they produce a steady flow of bubbles that disturb the surface. The filter plate on under gravel filters also limit's the composition of the gravel in which the plants are rooted. All other kinds of filtration systems will work well. The only things to be concerned about are if your filter causes too much disruption to the water surface.