The Fish That Actually Eats Hair Algae?

There aren't many freshwater fish I would recommend specifically for hair algae, but American Flag Fish have earned that reputation. They'll actually pick at the soft green strands growing through plants and across hardscape that many other algae grazers leave behind. For anyone who has spent an afternoon winding hair algae around a toothbrush, that's a pretty useful habit for a fish to have.

What makes them even more interesting is that you're not adding a fish that's only useful for cleanup. Mature males can develop an impressive mix of red, blue-green, and iridescent coloration, they're active throughout the aquarium, and they're one of the relatively few North American native fish commonly available to freshwater hobbyists. They're fun fish to watch even when the aquarium doesn't have an algae problem.

We've recommended American Flag Fish for hair algae for years, but there are a few things worth knowing before adding them. They have more attitude than an Amano Shrimp or Nerite Snail, mature males can be territorial, and baby shrimp are small enough to become food. None of that makes them a difficult fish. It just means we want to match them with the right aquarium.

What Makes American Flag Fish So Good at Hair Algae?

American Flag Fish spend a surprising amount of their day grazing. They'll move through the aquarium picking at plant leaves, rocks, driftwood, and other surfaces, and soft hair algae and filamentous algae are among the things they'll readily eat. This is different from many familiar algae eaters that are much better at cleaning films from hard surfaces than dealing with long strands of algae.

They can be especially useful after you've removed the worst of an outbreak yourself. If hair algae has already taken over a section of the aquarium, pulling out the large clumps gives the fish a chance to work on the remaining algae and new growth instead of expecting them to tackle a huge mess on their own.

You still want to figure out why the algae appeared. Long lighting periods, excess nutrients, inconsistent maintenance, or an imbalance in the aquarium can keep producing more algae than any fish could reasonably eat. We think of American Flag Fish as part of algae management rather than a replacement for good aquarium care.

They're also omnivores and need to be fed like any other fish. In addition to algae and biofilm, they'll eat small crustaceans, insect larvae, and other foods they encounter while foraging. We recommend a good prepared diet along with frozen and occasional live foods. Feeding them doesn't take away the natural grazing behavior that makes them so useful.

A Native Fish That Looks Great in a Planted Aquarium

American Flag Fish come from the southeastern United States, where they're found in slow-moving waters with plenty of aquatic vegetation. That background makes them particularly well suited to planted aquariums.

The plants aren't just there to make the aquarium look good. American Flag Fish spend a lot of time moving through them, inspecting leaves and grazing as they go. Dense growth also creates little breaks in the aquarium where fish can get out of one another's sight, which is useful when males begin establishing territories.

Mature males are where the common name really starts to make sense. Their coloration can include reds, blue-greens, iridescent scales, and darker markings that together are said to resemble the colors and pattern of an American flag. Females have more subdued coloration, but a group of males and females moving through a planted aquarium has a lot going on visually.

They're also a nice reminder that an interesting aquarium fish doesn't necessarily have to come from Southeast Asia, South America, or Africa. Having such a distinctive species native to our own part of the world is one of the things we've always liked about them.

They're Busy Fish

One reason we enjoy American Flag Fish is that they're rarely doing nothing. They explore plants, investigate hardscape, pick at surfaces, interact with other fish, and generally make good use of the aquarium.

That activity is also why tank mates matter. They aren't particularly well suited to very slow fish with long flowing fins. Long-finned Bettas, fancy Guppies, delicate Gouramis, and long-finned Angelfish would not be our first choices. A mature male can become territorial, particularly around breeding time, and long fins can invite chasing or nipping.

Active community fish are usually a better match. Rainbowfish, many peaceful Barbs, medium-sized Tetras, Corydoras Catfish, and other confident community species can all be worth considering. Aquarium size and individual temperament still matter, so there isn't a universal list that works in every tank.

When keeping several American Flag Fish, we like using plants, driftwood, and other hardscape to break up the aquarium rather than leaving one large open space where every fish can see every other fish. A male with multiple females can also work well when there is enough room and cover.

What About Shrimp?

This isn't necessarily an either/or decision. Adult Amano Shrimp and mature Neocaridina can often share a planted aquarium with American Flag Fish, and Amanos in particular can make a nice addition because they're working on different types of algae and biofilm throughout the tank.

Baby shrimp are a different situation. A shrimplet small enough to fit in a fish's mouth is potential food, and American Flag Fish are no exception. Plenty of plant cover can give young shrimp more places to disappear, but if the purpose of the aquarium is producing a large shrimp colony, we'd choose another fish.

For a planted community where you simply enjoy having some adult shrimp around, the combination can make much more sense.

American Flag Fish, Amano Shrimp, Nerites or Siamese Algae Eaters?

We get questions about all four because they're often recommended for algae control, but they aren't interchangeable.

Siamese Algae Eaters are very good algae grazers and another fish worth considering for hair algae. They're considerably larger as adults, though, so the aquarium that works for an American Flag Fish isn't automatically large enough for a Siamese Algae Eater.

Amano Shrimp are hard workers in a planted aquarium. They spend much of the day grazing algae, biofilm, leftover food, and other material from plants and hardscape. We like them as part of a cleanup crew, although a few Amanos aren't going to make a severe hair algae outbreak disappear overnight.

Nerite Snails are excellent for glass, rocks, wood, and decorations. They're one of our favorite choices for keeping those surfaces clean, but long strands of hair algae aren't really their specialty.

You don't necessarily have to choose only one. A planted aquarium can benefit from having different animals grazing different surfaces and different types of growth, provided they're all compatible with the aquarium and with one another.

What About Black Beard Algae?

This is one place where I wouldn't oversell American Flag Fish. You may see one pick at black beard algae, but their reputation for eating soft hair algae and filamentous algae is much stronger. If black beard algae is the problem you're trying to solve, I wouldn't purchase this species expecting it to clean it up.

Our Take on American Flag Fish

We originally became interested in American Flag Fish for the same reason many hobbyists do: they eat hair algae. That's still a great reason to consider them, especially because relatively few freshwater fish are willing to spend much time working on it.

What keeps them interesting after the algae is gone is everything else. They're colorful, active, curious fish that look especially good moving through a planted aquarium, and having a species native to the United States is pretty cool too.

We just want customers to know what they're getting. Give them active tank mates, some room to establish territories, plenty of plants and structure, and don't expect baby shrimp to be ignored. In the right aquarium, there isn't much not to like about them.

Frequently Asked Questions

Do American Flag Fish really eat hair algae?

Yes, and this isn't just a case of them occasionally picking at it. Hair algae and other soft filamentous algae are something American Flag Fish will actively graze as they move around the aquarium. It's one of the main reasons this species has become so well known in planted tanks.

What kind of algae do American Flag Fish eat?

Soft green hair algae and similar filamentous algae are where we've found them most useful. They'll also spend time grazing other soft algae and biofilm from plants and hardscape. Black beard algae is much less dependable, and we wouldn't buy them specifically for that.

How long will it take American Flag Fish to get rid of hair algae?

There really isn't a good number of days we can give you. A little new growth is very different from a tank where hair algae has been growing unchecked for months. If it's bad enough that you can remove large clumps by hand, do that first. The fish are much better at keeping up with manageable growth than cleaning up an aquarium that's completely overgrown.

Will they eat algae off live plants?

Yes. You'll often see them working over leaves and picking at whatever they find there. This is one reason we like them in planted aquariums.

Will American Flag Fish eat my aquarium plants too?

This one deserves some caution. They are plant grazers and may nibble softer or tender plant growth, so I wouldn't promise that every plant will be completely ignored. If you have a carefully aquascaped tank with delicate plants, that's something I'd consider before adding them.

Can I keep American Flag Fish with Amano Shrimp?

Adult Amanos are generally a much better match than tiny shrimp. An adult Amano is a fairly substantial shrimp, while a shrimplet looks a lot more like food.

What about Cherry Shrimp?

Mature Neocaridina can often coexist with them when there's plenty of cover. The babies are where you're going to take losses. If you're trying to grow a Cherry Shrimp colony as quickly as possible, this isn't the fish we'd choose for that tank.

Can I keep just one American Flag Fish?

Yes. You don't have to keep a group to enjoy this species. Keeping several can be interesting because you get more interaction and breeding behavior, but it also means paying more attention to territories and giving them enough room to get away from one another.

Are males more aggressive than females?

Usually. Mature males are the ones we're most concerned about when it comes to territorial behavior, particularly once breeding starts. Plants and hardscape help because a fish being chased can actually disappear from view instead of just swimming to the other end of an open tank.

Will they bother my Corydoras?

Corydoras are generally a much more sensible tank mate than a slow, long-finned fish. They spend most of their time in a different part of the aquarium and aren't likely to be viewed the same way another similarly shaped fish might be. As always, individual fish can surprise you, so watch the tank when introducing anything new.

Are American Flag Fish good for beginners?

Yes, as long as the beginner knows they're buying an active fish with some territorial behavior and not a passive algae-cleaning animal. Their actual care isn't especially difficult.

What happens when they've eaten all the hair algae?

You feed them. They're omnivores, not specialized algae-eating machines, and should already be receiving a normal diet while they're grazing algae. The nice part is that they'll usually continue browsing the aquarium for new growth even when they're being fed regularly.