Although you have followed directions and the water is at the proper pH and salinity (or specific gravity) when first mixed, check it with a hydrometer again at various intervals to make sure changes do not occur. The pH should be within the range of 7.6 to 8.3 when properly adjusted. It may be best to start at the higher end of the range because the danger lies in the pH falling below the lower limit as the tank water ages. This is somewhat offset by the carbonate content of the marine tank (gravel, coral, etc.) and water changes. The specific gravity should be in the range of 1.020 (at about 86°F) to 1.024 (at about 68°F).
The pump can now be set up and the gang valves and other pieces of equipment placed in position. The plastic tubing should be measured, cut (usually allowing a little slack), and attached. It might be a good idea to place a non-return or one-way valve in the line from he pump to prevent salt water from reaching the pump mechanism in case of a back-flow for any reason.
The glass or plastic cover for he aquarium can be placed on top and the pump, filters, etc. started. Normally, with a combination of filters and airstones there will have to be some adjustments made with the valves to get the proper flow of air to the various pieces of equipment.
Adjust the thermostat of your heater to the proper setting: about 76°F is ideal, but within a range of 69° to 82°F is acceptable. An aquarium thermometer is good to have handy, and there are a wide variety to choose from.
The light can be placed over the cover glass and turned on to see if your tank will be properly illuminated. The position (front or back) is optional. Some people prefer the light coming from the front of the tank so that they can view the fishes by the more desirable reflected light; others place the light on the back of the tank, leaving the front area free for feeding or other chores. Once everythig is set up and functioning properly, your should take a few moments
Your selection of fishes, as a beginner, must be basically oriented toward the hardier species. For examples, pomacentrids in general are very hardy fishes. These are beginner's fishes, including such diverse groups as the damselfishes, humbugs, and anemone or clownfishes. Smaller groupers are also popular with beginners, some being quite colorful and most being quite hardy. Beginners might also choose from a variety of triggerfishes and filefishes, lionfishes, gobies, and even some of the very colorful angelfishes. When you get more experienced with the hardier fishes you might try some of the wrasses, tangs, or even butterflyfishes. The size of the tank must dictate harshly how many fishes you can purchase. It is advisable to keep your tank underpopulated, at least at first. A general rule of thumb is to calculate an inch of fish for every 2 gallons of water, but there are so many variables that this rule is not easily applied. The bulk of the fish, its activity, feeding habits, all modify this rule.