Clean-up fish and invertebrates
Organisms that help keep the aquarium clean by eating algae, debris and food scraps. A complement to maintenance, not a replacement.
Detailed explanation
The most effective algae eaters in freshwater aquariums are: Otocinclus (green algae on surfaces), Siamese Algae Eater (filamentous algae and BBA), Amano Shrimp (all-rounder), Neritina (algae on glass).
In marine aquariums the CUC (Clean Up Crew) includes: Trochus and Astrea snails (algae on the rocks), emerald crabs (Valonia), Diadema urchins (algae), Lysmata shrimp (debris), Nassarius (debris on the bottom).
No fish or invertebrate cleans a dirty aquarium. They are a complement to regular maintenance, not a replacement. Don't buy a pleco thinking it will keep your tank clean without water changes.
The quantity must be calibrated on the volume of the aquarium and on the quantity of algae/debris. Too many cleaners = not enough food for everyone.