How old is the tank and whaat are your water parameters? Once the NH3
levels are zero and the nitrates are lowering, then would be the time to get a "crew" started. Make sure they are properly >>acclimated
<< via the "drip" method.
Here are some you could look at:
great for detritus and the sand bed.
especially good at film algaes..
cleans both the glass and the sand bed..
cleans up the uneaten food bits as well as detritus.
another excellent algae eater..
How many of each would really depend on the amount or detritus and algae that needs controlling. You do not want the animal load to exceed the natural food source. For now I would start with 20-30 mixed snails and see how that does for your tank.