A saltwater aquarium can provide great visuals for a room due to the vivid coloration of saltwater fish and invertebrates. In addition, saltwater fish are great pets as long as you care for them properly. If you are interested in starting a saltwater aquarium, you must first ask yourself if you can afford it and if you have the time to devote to setting up and maintaining the aquarium properly. This is VERY important because if you don't have either of these conditions, you will not be able to take proper care of the animals. You must also accept that it will probably cost more than you estimate, because most saltwater aquarium owners become addicted, with some setting up 3 or more tanks in their homes.
Many people do not realize the complicated factors involved in the survival of saltwater animals. You have to maintain safe and fairly stable levels of salinity (salt concentration), temperature, pH, ammonia, nitrites, and nitrates. If you are planning on keeping coral, some species of coral are highly sensitive to these parameters. However, it should be noted that some species of fish and coral are more tolerable than others as far as water parameters go. If you fail to maintain safe parameters, your fish will probably die.
You should also realize that saltwater aquariums cannot contain as many fish as freshwater aquariums because the oxygen levels are lower in saltwater. Some freshwater tanks are densely stocked with goldfish, but you will never be able to do this in a saltwater aquarium. Saltwater aquariums are also much heavier than freshwater aquariums due to the increased density of saltwater and the sand and rocks that you need to put in the tank, so make sure your floor can support a tank that weighs 1000 pounds or more.
Finally, depending on the type of fish and coral you get, you might have to deal with unique feeding requirements. There are herbivores and carnivores and some fish and invertebrates are so picky that they will only eat certain frozen foods. If you have coral, you will need strong lighting and maybe some calcium supplements. In many cases, you can't just toss some flakes in the water like you would with a freshwater tank.
If you can accept all of this and are prepared for a challenge, I will now explain how to go about setting up a saltwater aquarium. The first step is to decide how big of an aquarium you want. There are many sizes, but I highly recommend going with the biggest tank you can afford and fit into your housing. If you buy a bigger tank, you will have more stable water parameters and you will be able to get a larger variety of fish and coral. With a nano, you might be stuck with a few fish and certainly nothing as big as the popular yellow tang. Tanks come in glass and acrylic, but if you are going big (75 gallons or more) you are probably better off with acrylic. Also, if you are getting a big tank, it would be wise to get one that is drilled with an overflow, so you can set up a filtration system out of sight.
Once you have a tank, you have to get some lighting. Lighting is very important when it comes to coral because coral gets its energy from the light. If you are only getting fish you can get by with cheap fluorescent lights, but if you are planning on coral you will be better off with metal halides. In any case, the brighter the better and you will probably want to get some actinic (blue spectrum) lights since many coral and fish fluoresce under actinic lighting. A good choice in my opinion is a T5 or T5/metal halide combo lighting system that stands on top of your tank. Get a light timer as well, since you need to simulate light and dark so the fish can sleep and the invertebrates can clean the tank.
You will also need some heaters to keep the water warm. It is best to get two heaters because it will make the temperature more uniform and you have a backup in case one fails. Don't go cheap with heaters because you don't want electricity in the water and you don't want failures because heat is very important.
You will also need some powerheads (submersible water pumps) to move water around. Without water circulation, oxygen will not get into the water and you will have stagnation where waste collects. You want to have a good amount of flow, but not so much that your fish are constantly fighting the current.
For filtration, the best way to go is to use the Berlin method, which uses biological and mechanical filtration. The components of this system are live rock, live sand, and a protein skimmer. Live rock is basically rock taken from the ocean that is covered with the algae, bacteria, and other little invertebrates that clean up the water. Live sand is similar, only it is sand and usually contains different creatures, such as worms. The protein skimmer is a device that aerates water to get it to bubble up. It operates on the principle that waste proteins from fish go to the surface of the water and can be "skimmed" by bubbling the water into a cup.
Protein skimmers are important and it is a good idea to go with a quality model for the best water quality. You will occasionally have to empty the cup, which is stinky and fills with a brown/gray goo. Live rock and sand require no extra maintenence. Start by finding a protein skimmer and purchase the live rock and sand when you have your aquarium set up.
Finally, you will also need to buy some salt. No, you cannot use table salt! Specially formulated aquarium salt is available at reasonable prices online or in pet stores. Also buy a refractometer and some testing kits so you can check levels of nitrates, nitrites, and ammonia.
After you have your aquarium, set it up, ensuring that you have it where you want it. A filled aquarium cannot be moved due to its weight and structural concerns. Set up all the equipment and fill up about halfway with saltwater. Make sure that the protein skimmer, lighting, powerheads, and heaters are working and have the water at the correct temperature.
If you are buying live sand, you can add it directly to the water, but if you are buying dead sand (dry), you will need to rinse it a few times to get ride of tiny grains that could cloud your water. After adding the sand to the aquarium, let it sit for a few days so it all settles to the bottom. Now you can add the live rock. You can buy live rock online or from some stores or friends. If you buy live rock online it is shipped to you overnight, but it will still work. The benefit of buying from a local store or friend is that you won't have a lot of organisms die from the trip and foul your water. In either case, add the rock to your water, ensuring that you have 1.25 - 1.5 pounds per gallon of tank size. Make sure that the rocks are stacked in a stable manner since a falling rock can shatter the tank bottom.
Now that there are living things in your aquarium, you have to make sure that the salinity is stable. Since salt does not evaporate, you just have to worry about adding fresh water (NO SALT) to the aquarium to maintain the same salinity. As water evaporates, the salinity rises, so your goal is to replace the evaporated water. Additionally, now you can do 25% water changes every month or so. This entails removing 25% of the water and discarding it, then replacing it with freshly mixed saltwater. Water changes help by removing nitrates and other waste.
With the live rock and sand in the aquarium, you now have to wait for the system to stabilize. You have just added organisms to otherwise clean water and it will take a while for the bacteria to reach a stable level. When you first add the live rock and sand, you will see an ammonia spike, followed by a nitrite spike, followed by a nitrate spike. This process will take a month or more, but you must be patient. After you have 0 ammonia, 0 nitrites, and safe levels of nitrates, you can start adding fish.
It is good to start with a hardy fish, and I strongly recommend the green chromis, which is docile and hardy. You can also start adding some inverts, like blue leg hermit crabs and astrea snails, which will eat algae, fish waste, and leftover food. After adding these initial animals, wait a good month or more before adding any additional fish. If you add too many fish at once, you will have an ammonia spike since there will be too much waste without enough bacteria to process it. By adding one or two fish at a time, there will only be a small spike that will generally be harmless. After several months, you can start adding hardy coral, like mushrooms and leathers.
There you go, you should now be a successful saltwater aquarium owner! Remember, this is only a basic guide and you can learn much more by browsing saltwater aquarium forums and reading about the various creatures and equipment. I recommend going with reputed online dealers like Doctors Foster and Smith since they carry everything you will need to get your tank started. I also highly recommend that you buy aquacultured fish and coral, so you aren't stealing them from the ocean. Aquacultured fish and coral are reproduced by hobbyists and stores and, although only some species are available, progress is always happening.