In our opinion the best time to add a cleanup crew to your aquarium is after the tank has cycled, and the tank has begun showing algae. Both conditions should be met before adding a cleanup crew to your tank. Usually a tank is finished cycling by the time algae begins to form in the aquarium but that is not always the case.
Diatoms, a brown powdery algae like life form, are usually the first to show up in a new aquarium. When they begin to appear, you can begin adding a clean up crew to your aquarium. Snails that are good at removing diatoms include Ceriths, Nerites, and Astraeas.
At this stage, it is usually uncommon to have more complex algae in your tank such as hair algae, bubble algae or turf algae. Because of this cleaners that specialize in those areas such as hermits, turbo snails, or urchins should be avoided in a starting cleanup crew. Sometimes live rock added to a new aquarium will have those kinds of algae on them, in that case this general rule wouldn't apply.
Scavengers can be added with your starting crew if you plan to have fish or coral soon that you will be feeding. Scavengers can be fed sinking pellet food to tide them over if the tank is not receiving enough regular feeding to sustain them. When target feeding scavengers such as Nassarius snails or starfish it is important to remember they have slow metabolisms compared to fish - feed sparingly and infrequently. (Once or twice a week tops).
Certain cleaners, such as chitons, limpets, and urchins should be avoided in starting crews because they have less tolerance to poor or unstable water conditions relative to other cleaners that can equally do the job in a young tank.
A cleanup crew can be added in stages, or all at a time (assuming the limitations discussed in this article are followed), without a major impact to the bio load of the tank. This is because of the slow metabolism and low oxygen consumption of algae eating invertebrates used in standard cleanup crews when compared to more active fish.