Cleaner fish for aquariums: the clean-up crew myth explained

You'll hear it in almost every fish store: "Get this one, it'll keep your tank clean." Corydoras, plecos, otocinclus, shrimp and snails are sold as if they were a cleaning service with fins. It's one of the most widespread myths in the hobby and one of the deadliest, because many of these "cleaners" end up starving or outgrowing tanks that are far too small. The truth is simple: no fish or invertebrate cleans the tank for you. Some help with algae or pick up leftover food, but they also eat, produce waste and have their own needs. This guide covers what each one really does.

Why the "cleaner fish" is a myth

What we call dirt in a tank is really three different things: waste (fish poop, uneaten food, dead leaves), dissolved compounds (ammonia, nitrite, nitrate) and algae. No animal eats poop or removes nitrate. Quite the opposite: every fish you add produces more waste and more nitrate. Algae appear because light and nutrients are out of balance; an algae eater can slow them down, but if you don't fix the cause they come back.

Animal	What it really does	What it doesn't do	Adult size	Suggested tank
Corydoras	Sifts sand and picks up leftover food	Doesn't eat poop or algae	1-3 in (3-7 cm)	15 gallons (group of 6+)
Bristlenose pleco	Rasps soft algae and biofilm off glass and wood	Doesn't clean the substrate or remove tough algae	5-6 in (12-15 cm)	26-30 gallons
Common pleco	Eats algae when young; as an adult, mostly food and wood	Makes far more mess than it cleans	12-20 in (30-50 cm)	100+ gallons
Otocinclus	Grazes diatoms and soft algae on leaves and glass	Can't survive without algae and extra food	1.5-2 in (4-5 cm)	15 gallons, mature (group of 6)
Amano shrimp	Eats soft hair algae and leftovers	Won't wipe out a major algae outbreak	1.5-2 in (4-5 cm)	10 gallons
Nerite snail	Scrapes diatoms and green algae off glass and rocks	Doesn't eat poop or large debris	1 in (2-3 cm)	5 gallons

Corydoras: scavengers, not janitors

Corydoras such as the bronze cory or the panda cory spend all day rooting through the substrate with their barbels. It looks like cleaning, but they are hunting for food: they eat leftovers that fall to the bottom and leave poop alone. They are social fish that need groups of at least 6 of the same species, fine sand or smooth gravel (sharp, dirty gravel wears down their barbels) and clean water, because they are sensitive to high nitrate.

The big mistake is not feeding them "because they eat the leftovers". If the other fish are fast at the surface, almost nothing reaches the corys. They need a sinking bottom feeder food such as wafers or pellets, ideally right after lights out.

Plecos and otocinclus: size and hunger

With plecos, size is everything. The bristlenose pleco tops out at 5-6 inches (12-15 cm) and is a good choice for tanks of around 30 gallons: it rasps soft algae but also needs driftwood to chew on, algae wafers and blanched vegetables (zucchini, cucumber). The common pleco (Pterygoplichthys), on the other hand, is sold at 2 inches and easily reaches 12-20 inches (30-50 cm). As an adult it loses interest in algae, eats everything and produces a huge amount of waste.

The otocinclus is a tiny 1.5-2 inch catfish that excels at eating diatoms (the brown algae of new tanks) and soft algae. Its problem is the opposite: it's so small and specialized that many starve, and plenty arrive at the store already weak. Add them only to a mature, planted tank with some algae, in a group of 6 or more, and offer algae wafers and blanched zucchini from day one.

Amano shrimp and nerite snails

The Amano shrimp is probably the best real clean-up crew: it eats soft hair algae, biofilm and leftover food, and works in groups. Even so, it won't perform miracles on tough algae like black beard algae, and if you feed lots of prepared food it will prefer that to algae. It needs a copper-free tank without large fish that would eat it.

Nerite snails scrape diatoms and green algae off glass, rocks and tough leaves without harming plants. They don't breed in freshwater, although females leave small, hard white eggs on decor that never hatch and are hard to remove. They like to escape, so keep a lid on. If the tank doesn't have enough algae, they also need algae wafers or vegetables.

They all need their own food

This is the most overlooked point. A well-kept tank has little algae and little leftover food, so the cleaners can't find enough to eat on their own. And once you feed them properly, they eat less algae, which is normal.

• Corydoras: sinking wafers or pellets, frozen food now and then.
• Bristlenose and otocinclus: algae or spirulina wafers, blanched vegetables and, for the bristlenose, driftwood.
• Shrimp and snails: biofilm, a little shrimp food and vegetables.

To get portions right without fouling the water, our guide on how much and how often to feed fish gives general rules.

No animal replaces maintenance

What really keeps a tank clean is a simple routine, and no fish can do it for you:

Task	How often	Tool
20-30% water change while vacuuming the substrate	Weekly	Gravel vacuum
Clean the glass	Weekly or as needed	Magnetic algae cleaner or scraper
Rinse filter media in tank water	Every 3-6 weeks depending on the filter	Bucket of old tank water
Trim plants and remove dead leaves	Every 1-2 weeks	Scissors and tweezers
Test ammonia, nitrite and nitrate	Weekly at first, then monthly	Water test kit

Our water change guide walks through the routine step by step, and if algae are what's bothering you, start with our guide to aquarium algae: fixing light and nutrients works far better than adding more animals.

Common mistakes

• Buying a fish "to clean" without checking its adult size.
• Putting a common pleco in a 15-30 gallon tank.
• Keeping one or two corydoras alone instead of a group.
• Not feeding cleaners because "they eat the leftovers".
• Adding otocinclus to a freshly cycled tank with no algae.
• Stacking up clean-up crew to hide an overfeeding problem.
• Skipping gravel vacuuming and water changes because you have "cleaners".

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