Before you jump into anything I would recommend you do a lot of research so you can see what you are getting into. Look up different tanks, what kind of corals and fish and inverts you want to stock, then build your tank around that. Some corals and fish are way more demanding than others and that will dictate what kind of set up you need. Besides the tank you are going to need a lot more to get started. Sand (unless you want bare bottom), Live rock, heaters, pumps, lighting, skimmer, Reverse osmosis/deionizer (RO/DI), salt, refractometer, test kits, and potentially much more. I would not recommend using tap water for anything (top off, or salt mixing). Use RO/DI water or buy water from your LFS (local fish store). A reef tank is a delicate ecosystem and your tap water might contain metals and other things that can build up over time and cause major problems in a reef tank. As far as water changes they are pretty straight forward. You make some RO/DI water then add a set amount of salt to a mixing container (buckets or garbage cans depending on the amount). Use the refractometer to make sure the salinity is correct and matches the salinity in the tank. Let it mix a while until it is clear (usually with a powerhead or some kind of pump). Heat it up to the correct temperature (notice I said heaters and pumps up above). Then you just pull a set amount of water out of the tank and replace it with the newly mixed salt water. You do this for a couple of reasons and it is real important to do. One is to get rid of the bad stuff that forms in the tank that comes from the fish poop, fish food, and anything else that rots (nitrates, phosphates, and other bad stuff). the second and probably more important is to replace all the elements getting used up by the corals and other organisms (calcium, magnesium and a plethora of trace elements). Its a real simple process but is a little time consuming because usually you will want to do other things at that time (vacuuming the sandbed, replacing filter media, carbon, GFO, filter sponges, removing and cleaning the pumps, cleaning salt creep off the lights and other equipment. That's why it takes time. Once again, research. Learn about the nitrogen cycle. Learn about lighting, par, pur, lux. Whats the optimal temperature? How will you cool your tank on hot days? Whats the ugly phase and how do you minimize it? Just make sure you know what you are getting into. The tank is the cheap part. All the other equipment costs a bit and maintain costs as well.
