You don't want to overload the system, otherwise a spike in ammonia will likely occur. One or two primary diatom and macroalgae eating fish, such as Tangs, Angelfishes, and Blennies, as well as some snails, hermit crabs and other hardy tank janitors are ideal additions at this point.
Stabilize the System
After you have added a few new additions to the aquarium, allow the system to run for several weeks to become stable before continuing on.
This means you should test the water daily for traces of ammonia and nitrite after introducing the first new animals. The longer you let the system run before putting anything else new in, the better, because this allows the beneficial bacteria to mature and multiply, making the biological filter base stronger.
When all looks good, go ahead and add a few more new pieces of livestock as you did before.
