The first type of saltwater aquarium is the fish only aquarium. This is probably the easiest to care for of the five types, simply because you are only dealing with one type of species. Amongst the saltwater fish there are both tropical and coldwater types. They can't be kept together for obvious reasons. Once the tank is established and the chemical levels are stable, it will stay that way, and you shouldn't need to test it if you do frequent water changes. 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. Therefore they are being considered for the endangered species list. It would be irresponsible to attempt to house one of these creatures, unless fully educated on their care needs. Sand sharks adapt the best of all sharks to a captive environment. The types of aquariums that house these very large fish are usually public state supported aquariums. If you have additional light sources aside from the tube in the hood, bubble coral should do well anywhere in the tank. If you are using the included florescent tubes for lighting, it may be better to place the coral closer to the surface. This species of coral prefers low movement of the water. Be sure not to place it in any direct current. More recently glass tanks have become less frequently used due to the flexibility of acrylic. Literally flexibility! Acrylic aquariums are far more for forgiving than there glass counterparts. If a heavy object strikes a glass tank, it will almost certainly break. The flexibility of an acrylic tank will prevent this catastrophe from happening. 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.