"Sweeper fish" is a loose term hobbyists use for bottom-dwelling and algae-eating fish that clean up uneaten food, algae, and debris from the aquarium substrate and glass. The most common options are plecos, Corydoras catfish, otocinclus, and in some contexts, loaches. The right sweeper fish for your tank depends on tank size, water type, and what you're trying to clean up. This guide covers each major option, what they actually eat, and how to make sure they're getting enough food rather than slowly starving.
One thing worth knowing up front: sweeper fish are fish first, cleaning crews second. They won't solve an algae outbreak caused by too much light or excess nutrients. They supplement a healthy tank, they don't fix an unhealthy one.
Common Sweeper Fish for Freshwater Tanks
Bristlenose Pleco (Ancistrus sp.)
The bristlenose pleco is the most practical algae-eating fish for most hobbyists. Unlike common plecos (Pterygoplichthys pardalis) that grow to 18-24 inches and require tanks of 75+ gallons, bristlenose plecos max out around 4-6 inches and do well in 30-gallon tanks and up.
Bristlenose plecos graze on soft algae, biofilm, and leftover plant matter. They work glass, rocks, and hardscape. They need supplemental feeding of sinking wafers (Hikari Algae Wafers or Omega One sinking pellets) because the algae in a clean tank isn't enough to sustain them. Add a piece of driftwood to their tank as well. Bristlenose plecos actually consume driftwood fiber as part of their digestive process.
Water parameters: 72-80°F, pH 6.5-7.5, moderate hardness. They're hardy, peaceful with most community fish, and long-lived. A well-kept bristlenose often lives 10-12 years.
Otocinclus (Otocinclus vittatus / O. Affinis)
Otocinclus are small (1.5-2 inches), peaceful catfish that specialize in soft green algae and diatoms on glass and plant leaves. They won't touch hair algae or hard spot algae, but for the soft brown film that forms on glass in new tanks, they're excellent.
The catch is that otocinclus are delicate when first purchased. Most wild-caught otos arrive stressed and underfed from collection and shipping. Many die within the first week if not given an established, stable tank with soft algae already growing on surfaces. Don't buy them for a new, uncycled tank.
Keep them in groups of at least 5-6. Solo oto catfish stress easily and often refuse to eat. They do best at 72-78°F with soft to moderately hard water and a well-planted environment.
Corydoras Catfish
Corydoras are bottom feeders rather than algae eaters. They scavenge uneaten food from the substrate before it rots and contributes to ammonia spikes. That makes them "sweepers" in the sense of keeping the bottom layer clean, though they don't eat algae.
There are over 150 species of Corydoras. The most common aquarium species are Corydoras paleatus (peppered cory), Corydoras sterbai (Sterbai cory), and Corydoras aeneus (bronze cory). All prefer groups of 6 or more and smooth, fine substrate that won't damage their barbels. Avoid sharp gravel.
They're completely peaceful and mix well with almost any community fish. Temperature range varies by species: most tropical Corydoras prefer 72-78°F, while Sterbai corys do best at 78-82°F.
Sweeper Options for Larger Freshwater Tanks
Common Pleco (Pterygoplichthys pardalis)
The common pleco is what most beginners think of when they picture an algae eater. They're sold small at 2-3 inches but grow fast. A 12-inch pleco in a 30-gallon tank is a common story, and it doesn't end well for the fish.
Common plecos belong in tanks of 75 gallons minimum, with 100+ gallons preferred for adults. They're effective algae cleaners but produce enormous amounts of waste for their size. In the right setup, they're impressive fish. In a too-small tank, they suffer.
Siamese Algae Eater (Crossocheilus oblongus)
The Siamese algae eater is notable for being one of the few fish that actually eats red algae (brush algae), which most other algae eaters ignore. They're active swimmers that graze on glass, rocks, and hardscape throughout the tank.
They reach 6 inches and do best in tanks over 30 gallons. One important note: there are several species sold under the "Siamese algae eater" name, and some imposters, including the Chinese algae eater and the false SAE, don't eat algae and become aggressive as adults. The true Siamese algae eater (C. Oblongus) has a solid black stripe extending into the tail fin, which distinguishes it from impostors.
Saltwater Sweeper Fish and Cleanup Crew
In saltwater tanks, the term "cleanup crew" is more common than "sweeper fish." The cleanup crew usually combines invertebrates (hermit crabs, snails, urchins) with fish that eat specific types of waste or algae.
Blennies
Lawnmower blennies (Salarias fasciatus) are the closest saltwater equivalent to the bristlenose pleco. They graze on microalgae and diatoms on rocks and glass. They need an established tank with enough algae to sustain them and occasional supplemental feeding of algae sheets. They reach about 5 inches and need a tank of at least 30 gallons.
Tangs
In larger reef tanks (75+ gallons), tangs are some of the most effective algae-grazers available. The Pacific Blue Tang (Paracanthurus hepatus), Yellow Tang (Zebrasoma flavescens), and Tomini Tang (Ctenochaetus tominiensis) all graze constantly on different algae types. Tangs need substantial swimming space and a varied algae-based diet.
Wrasses
Certain wrasses act as cleanup crew in a different way. Six-line wrasses (Pseudocheilinus hexataenia) and leopard wrasses hunt small worms, copepods, and parasites that other fish ignore. They're not algae eaters but they reduce parasitic loads and consume detritus-dwelling organisms.
Feeding Your Sweeper Fish Properly
This is where most people go wrong. They add a pleco, otocinclus, or Corydoras and assume the tank provides enough food. In most setups, it doesn't. Algae grows slowly in a healthy, well-lit tank, and a healthy pleco needs more than a few algae patches to thrive.
Supplemental Feeding Options
Sinking wafers: Hikari Algae Wafers, Omega One Veggie Rounds, and New Life Spectrum Bottom Feeder pellets are all well-regarded options. Drop one or two into the tank after the lights go off so catfish have access before other fish investigate.
Blanched vegetables: Zucchini, cucumber, and spinach attached to a veggie clip give bottom feeders a fresh food source. Bristlenose plecos and common plecos especially enjoy zucchini slices left overnight.
Frozen foods: For Corydoras and carnivorous sweepers, frozen bloodworms and daphnia encourage natural foraging behavior. Feed small amounts 2-3 times per week as a supplement.
If your Corydoras have thin, wasted bellies or your pleco has a sunken stomach, they're not getting enough food. These are common signs of slow starvation that new hobbyists miss.
To stock your tank properly, our Best Online Fish Supply Store guide covers where to find quality fish and the foods they need.
For keeping the tank environment clean between water changes, an oxygen machine for fish tank improves water circulation and helps bottom feeders access oxygenated water.
Setting Up the Right Environment
Bottom feeders need places to hide and rest during the day. Caves, driftwood, and densely planted areas give plecos and Corydoras the cover they need to feel secure. A pleco without hiding spots will spend most of its time in a corner, stressed.
For substrate: smooth sand or fine gravel protects Corydoras barbels, which can erode on sharp gravel. Coarse gravel can cause visible barbel damage within weeks.
Flow: Most bottom-dwelling sweeper fish appreciate moderate to strong flow, which mimics their natural river environments. This also keeps detritus from settling into deep substrate layers where Corydoras can't reach.
FAQ
How many algae eaters do I need for a 50-gallon tank?
For soft algae on glass and hardscape, 4-6 otocinclus or 1-2 bristlenose plecos will handle a 50-gallon tank. For substrate debris, 6 Corydoras catfish are a solid cleanup crew. Don't overstock solely for cleaning purposes because every fish adds bioload. A small cleanup crew plus regular maintenance works better than crowding the tank with bottom feeders.
Will sweeper fish eat all my algae?
Different fish eat different algae types. Bristlenose plecos and otocinclus handle soft green algae and diatoms. Siamese algae eaters target red/brush algae. No fish consistently eliminates hair algae, cyano (blue-green algae), or hard spot algae. Fixing the underlying cause (excess nutrients, too much light) is the only reliable solution for problem algae.
Can I keep sweeper fish with my community fish?
Most sweeper fish are peaceful and compatible with standard community fish. Corydoras, bristlenose plecos, and otocinclus all work well alongside tetras, rasboras, and livebearers. Avoid keeping common plecos with small fish they can trap against the glass, and avoid keeping large, aggressive cichlids with small, docile bottom feeders.
Do I still need to clean the tank if I have sweeper fish?
Yes. Sweeper fish reduce maintenance but don't eliminate it. You still need regular water changes, filter cleaning, and substrate vacuuming. In fact, adding bottom-dwelling fish increases your bioload, which can mean more frequent water changes if the tank is already near capacity. Think of sweeper fish as one part of a maintenance system, not a replacement for it.
Bottom Line
The best sweeper fish for most freshwater community tanks are bristlenose plecos for algae on glass and hardscape, and Corydoras catfish for substrate debris. Otocinclus work well for soft diatom algae in mature, established tanks. Make sure every fish in your cleanup crew is getting adequate supplemental food, because relying on tank algae alone leads to slow starvation. Match your sweeper fish to your tank size, keep hiding spots available, and you'll have a noticeably cleaner tank with minimal extra effort.