The following biological bacteria seeding method will help to cut a substantial amount of time (weeks, in most cases) required to establish the biological filter in a saltwater aquarium.
The nitrogen cycling process that all new saltwater aquarium (and freshwater aquariums) set ups go through when they are first started is what leads to the birth of the aquarium's biological "bacteria" base. From start to finish, this cycle usually takes around 30 to 45 days to complete its mission, and depending on each individual aquarium's set up and care variables, sometimes longer. There are several methods to greatly reduce the cycling time on an aquarium.
An aquarium is considered to be "cycled" when two forms of bacteria (nitrobacter and nitrosoma) are present in quantities which will process the ammonia (NH3) into nitrites (NO2) and then into nitrates (NO3), leaving no detectable nitrites.
If you don't want to wait around for nature to run its course and create this needed end result bacteria, there are ways to help speed up the cycling process by "seeding" a new tank with mediums or materials that already have a mature bacteria population established on them. Seeded live rock is an excellent source of bacteria and due to its porosity, it can carry a huge quantity of bacteria which will be buried in all of the nooks, crannies and minute holes in the rock.
These seed sources are usually obtained by removing them from another saltwater aquarium that is well established, one at least 6 months old, and is disease free, meaning one that is not suspect of having or is undergoing treatment for a disease of any kind. Good sources for seeded live rock are your local fish store, if they have rock which has been in a functioning saltwater aquarium for a period of time or a friend's tank which has been running for a period of time.
When transferring the live rock from the established tank, many people will scrub the rock to remove any algae and dead or decaying material. While removing as many unwanted "hitch hikers" (i.e. Bristleworms, Mantis Shrimp, etc.) as possible is a good idea before transferring the rock, it is usually best to not scrub the rock to remove all of the algae as this will remove a lot of the beneficial bacteria, which will defeat the purpose of using the seeded rock.
Other tank materials such as Live Sand or sand substrate or even aquarium decoration from another established saltwater aquarium can also be used to transfer live bacteria and establish the biological filter bed in a new tank. These materials will carry the same bacteria as the live rock and will help to cut the cycling time of the new tank.
Once the live rock is transferred to the new tank, the bacteria will require a food source (ammonia) in order to reproduce and populate the surface areas in the tank. While is is safe to place a few fish in the tank to provide the ammonia source it is best not to load up the system with livestock too quickly as this will produce more ammonia than the relatively small population of bacteria can immediately handle. Testing the aquarium water for ammonia, nitrites and nitrates on an almost daily basis will help you to determine how well the bacteria population is increasing as you go along. If the ammonia levels are rising too quickly and approaching the danger zone, you can quickly reduce the levels with a dose of an ammonia removal product such as Amquel to keep the level in the safe zone.
There are a number of other sources for the ammonia required to feed the bacteria, other than just fish. Invertebrates such as Hermit Crabs, True Crabs, and Shrimps which you are planning to add to the tank will consume food and produce ammonia. Placing these Reef Tank Safe Janitors in the tank to begin with will also go a long way towards reducing tank maintenance in the future.