Plecos and corydoras catfish are the most common tank cleaners, but neither eats poop directly

The short answer is that no fish actually eats waste the way many aquarium guides claim. Plecos (armored catfish) and corydoras catfish are sold as "cleanup crew" fish because they scavenge uneaten food and dead plant matter off the bottom. They do not digest fish waste. What they do is reduce the amount of rotting food that would otherwise break down and foul the water — which indirectly keeps the tank cleaner.

Fish waste (poop) breaks down into ammonia, which is toxic to fish. The only things that actually remove it are your filter's beneficial bacteria and regular water changes. No fish can solve that problem for you. Buying a pleco or corydoras will help with leftover food, but it will not replace maintenance.

Key Takeaways

  • Plecos and corydoras catfish eat uneaten food and algae, not fish waste, and they still produce their own poop that adds to the bioload.
  • Fish waste becomes ammonia in the water; only your filter's bacteria and water changes remove it — no fish can do this job.
  • Corydoras are better for smaller tanks because plecos grow large, produce heavy waste, and can damage plants and decorations.
  • Adding a "cleanup crew" fish without upgrading your filter or changing water more often will make water quality worse, not better.
  • Snails and shrimp also scavenge but add bioload; they work best in established tanks with strong filtration.

Why plecos don't actually clean the tank

Plecos are bottom feeders that eat algae wafers, sinking pellets, and leftover food. In the wild, they graze on algae and wood. In a tank, they do reduce the amount of decaying food sitting on the substrate — which is useful. But they produce substantial waste themselves. A large pleco can generate as much bioload as several medium fish, meaning you are trading one cleaning problem for another.

Plecos also grow much larger than most people expect. Common plecos reach 12 to 24 inches and live 10 to 20 years. They uproot plants, knock over decorations, and need tanks of 75 gallons or larger as adults. Smaller pleco species exist, but even they need 40 gallons minimum. If your tank is smaller, a pleco will stunt and suffer.

Corydoras catfish: a better choice for smaller tanks

Corydoras are smaller than plecos — most species stay under 3 inches — and they work well in 20-gallon tanks and up. They spend their time on the bottom sifting through substrate, eating uneaten food and dead plant matter. They are peaceful and do not uproot plants or damage decorations the way plecos do.

Like all fish, corydoras produce waste. They also need clean water and a good filter to survive. They are not a substitute for maintenance; they are a supplement. Keep the substrate clean by removing uneaten food within a few minutes of feeding, and corydoras will help finish what the fish miss. Without that baseline care, corydoras will just add more waste to an already dirty tank.

How fish waste actually leaves the tank

Fish poop contains ammonia, which is poisonous even in small amounts. Your filter removes it through two processes. First, mechanical filtration traps solid waste so it can be removed when you clean the filter. Second, beneficial bacteria in the filter convert ammonia to nitrite, then to nitrate, which is less toxic and can be removed by water changes.

This process takes time and depends on having enough bacteria in your filter. A new tank without established bacteria will not handle waste well, no matter how many cleanup fish you add. An overstocked tank will produce more waste than the bacteria can process, and water quality will crash. The only real solutions are a strong filter, regular water changes (usually 25 to 50 percent weekly), and not overstocking the tank.

Other scavengers that don't eat poop either

Snails and shrimp are also marketed as cleanup crew. Nerite snails eat algae and leftover food. Amano shrimp are excellent algae eaters. Both reduce the amount of decaying matter in the tank, which helps. But both also produce waste and add to the bioload. They work best in established tanks with strong filtration and regular water changes, not as a replacement for maintenance.

Snails can also reproduce rapidly if overfed, turning a cleanup crew into a pest. Shrimp need stable water conditions and can die suddenly if ammonia or nitrite spikes. Neither is a solution for a neglected tank.

What actually happens when you overstock with cleanup fish

Many aquarium owners buy multiple plecos, corydoras, snails, and shrimp hoping to avoid water changes. The result is a tank with more fish producing more waste, a filter that cannot keep up, and water quality that crashes. Fish become stressed, stop eating, and develop diseases. The cleanup crew dies first because they are sensitive to poor water conditions.

If you are considering adding cleanup fish because you want to do fewer water changes, do not. Instead, upgrade your filter, reduce the number of fish you have, or commit to weekly maintenance. A 20-gallon tank with 5 fish and a good filter will stay cleaner than a 20-gallon tank with 15 fish and a pleco.

How to actually keep your tank clean

Start with a filter rated for your tank size — ideally one rated for a tank 1.5 times larger than yours. Do a 25 to 50 percent water change every week. Remove uneaten food within a few minutes of feeding. Vacuum the substrate during water changes to remove settled waste. Do not overstock.

If you want a cleanup crew, add one corydoras or a few small snails to an established tank with good filtration. They will help, but they are not the main solution. The main solution is the filter, the water changes, and not feeding more than the fish will eat.

Frequently Asked Questions

Do plecos really eat fish poop?

No. Plecos eat algae, uneaten food, and plant matter. Fish waste breaks down into ammonia in the water column; no fish can remove it. Only your filter's bacteria and water changes do that. Plecos produce their own waste, which adds to the problem.

Can I skip water changes if I have a pleco?

No. A pleco does not remove ammonia from the water. It may eat some leftover food, which reduces one source of waste, but it produces waste itself. You still need weekly water changes and a good filter. Skipping maintenance with a pleco will result in poor water quality and sick fish.

What is the best cleanup fish for a 20-gallon tank?

Corydoras catfish are better than plecos for small tanks because they stay small and do not uproot plants. A few nerite snails also help. But the real cleanup is done by your filter and water changes, not by the fish. Add one or two corydoras to an established tank with good filtration, not as a substitute for maintenance.

Do snails eat fish poop?

No. Snails eat algae, uneaten food, and dead plant matter. They do not remove ammonia from the water. They also produce waste and can reproduce rapidly if overfed. Use snails as a supplement to maintenance, not a replacement.

How often should I clean my filter if I have cleanup fish?

The same schedule as any tank: usually every two to four weeks, depending on bioload and filter type. Cleanup fish do not reduce the amount of waste your filter has to process — they just eat some of the uneaten food before it decays. You still need to clean the filter regularly to keep beneficial bacteria alive.