How often should I clean my aquarium?

The answer to this rather generic question depends on the size and type of aquarium, the filtration with which it is equipped, the number of fish that are kept, and your definition of "cleaning." For most aquariums, if time allows, we recommend 10% water changes done once a week. If you use an under gravel filter, gravel on the bottom, or a bare-bottom tank, we suggest you vacuum out accumulated detritus and debris as you remove water from the tank. Do not vacuum a Jaubert (or plenum) system! Mechanical media in canister and other filters should be rinsed or changed every two weeks. Please note: Biological filter media used to support beneficial bacteria populations should rarely be cleaned, and should NEVER be cleaned in tap water. If biological media becomes clogged, it should be flushed in a bucket of water taken from the aquarium. Algae removal from the tank panels can be done on an as-needed basis, but no more than once a week. Remember that to your fish, your arm and hand look like a giant predator. Each time you reach into your tank, you stress the fish. Fish that get stressed too often get sick and eventually die!

What's the best way to vacuum the substrate in my tank?

You should vacuum the gravel in your tank as part of the process of removing water during a water change. Use a gravel washer. This is a 2" diameter tube that fits on a much smaller diameter vinyl siphon hose. Some tank cleaning systems hook directly to a sink and use water pressure to create a vacuum in the hose, allowing you to drain the water from your tank to the sink drain without carrying buckets. You should not vacuum the gravel through a filter and pump that puts water back into your aquarium.
Tanks equipped with under gravel filters should always be vacuumed at every water change. The substrate that is visible in reef tanks should be siphoned free of detritus at every water change. Care should be exercised not to disturb root systems when vacuuming substrate in freshwater planted aquariums.
Unless you have a reef aquarium or a planted freshwater tank, remove half of the decorations before you remove water from the tank for a water change. Put the other half at on end of the tank, to provide cover for your fish. Vacuum the substrate in rows from front to back, gravel-washing each row thoroughly before going to the next. The trick to gravel-washing is to wash as much gravel as possible while only removing the desired amount of water. If you have removed as much water as you want, but are not finished vacuuming, stop, redecorate, refill the tank, and take up where you left off on the next water change. 

Is there any other means of increasing salinity levels other than evaporation or a product like instant ocean?

Salinity is actually an incorrect term, though we realize many others have probably used it. The correct term is specific gravity, which is a measurement of how much dissolved solids are in water. The only way to increase the specific gravity is to add more salt. Even evaporation does not have much effect unless a lot of evaporation occurs.

How much water should I change and how often?

Water changes may be done on a regular schedule or as-needed according to water test results. For most aquariums, if time allows, we recommend 10% water changes, done once a week, regardless of test results. If you use an under gravel filter or a shallow layer of gravel on the bottom, we suggest you vacuum out accumulated detritus and debris as you remove water from the tank. At a very minimum, we suggest changing 25% of the water at least once every four weeks. If you are correcting a bad water condition and more than 25% of the water is to be changed, add new water back to the aquarium slowly or do smaller water changes every other day. For water changes in excess of 25%, add one inch of new water every ten minutes so as not to stress fish, or upset the environment. It is possible to change too much water or change water too often, and this happens more than you might think. Always remember that an aquarium should not be a sterile environment that is clean enough to drink out of!

How often should you add sea salt to your aquarium?

You should never add salt to your aquarium without doing a water change. Salt does not evaporate and if you keep adding salt, the salinity will rise to dangerously high levels. Do a 25% water change once a month, or change 10% every week or two weeks, by removing some saltwater and adding new water. When removing water, you should vacuum the substrate (gravel). When your tank evaporates, you should only add plain water, with no salt added.