An Easy Guide for Aquarium Algae

Posted by Augusta Hosmer on

Read Time: 9 mins

AKA: More Than You Ever Wanted to Know About Algae and Then Some

Algae and pond/aquarium hobbyists have been at war for centuries. It's not always the ultimate opponent like many people think, but it can be a royal pain if it takes hold. Fortunately, we have an analgesic (an-algae-sic?) with the info in this article. We'll cover why and how algae takes over your tanks and ponds, types of algae, and treating/preventing excess algae. 

Why Algae Can Cause Such a Headache

First off, understand that algae is kind of a plant, kind of not, so you have to approach it that way when it’s in your ponds or planted tanks. When I first got into plant biology, I had no idea I’d be stepping into a decades-long beef about what algae is, but here we are (if you ever think science is boring, go sit in on a conference where scientists don’t agree on an organism classification. Bring popcorn).

The general population’s perception of algae is that it’s a plant, which makes sense. It utilizes photosynthesis (using light to make energy for itself), its cells contain chloroplasts (little, disc-shaped parts of the cell that make photosynthesis possible), it needs the same essential nutrients as plants, and recent research indicates algae has genes that are also present in plants or have counterparts in plants.

That said, algae doesn’t have many of the structures traditional plants have, they’re almost always aquatic when most plants are terrestrial, they’re a lot more mobile, and they absorb nutrients directly from the water instead of via roots. They also use different pigments to absorb light. Because of this, biologists often classify algae as a “plant-like protist” instead of a plant. 

Why even bring this up? Because algae’s differences allow it to do what your aquarium plants do, only better. Photosynthesis, surprisingly, isn’t that efficient even though it makes the world go round. Plants and algae can only convert a fraction of the light available to them into energy, and algae converts a higher percentage than true plants.

The “too long, didn’t read, I don’t like science” version: it grows more quickly and more easily than your aquarium plants and can get out of control easily as a result.

Types of Algae (some aren’t even really algae)

Knowing what kind of algae you have can help you figure out how to deal with it. There are thousands of algae species, but the ones affecting ponds and aquariums are broken down into a few main groups:

  1. FILAMENTOUS ALGAE is thread-like and forms thick, green and yellow clumps and mats. It can take over your water surface and tank décor. If you ever reach into a tank and pull out fistfuls of what looks like green hair, you’re probably dealing with a filamentous algae species like water silk/blanketweed (Spirogyra, Clado), or black beard algae (Audouinella
  2. PLANKTONIC ALGAE free floats. It’s the cause of green "pea soup" water.
  3. MICROALGAE includes brown algae/brown diatom (Phaeophyceae and Bacillariophyceae) that coats your tank walls and decor in brown; and bottom-dwelling skunkgrass/muskgrass (Chara) that's often confused with aquatic plants
  4. CYANOBACTERIA is also called blue-green algae, but is not technically algae. It’s caused by photosynthetic bacteria, and it covers your tank in a layer of blue, turquoise, sometimes even black-looking slime.

    The video above is a good example of a LOT of filamentous algae. 

Cause of Algae in Aquariums and Ponds (And How to Keep it from Going Crazy)

Algae gets out of control in environments with excessive/insufficient nutrients, carbon dioxide, and light. You want plenty of these things if you have live aquatic plants. But you don’t want to blast your tank or pond with resources. Similarly, you don’t want too few, or too much of one and not enough of another. The crux of the entire aquatic hobby is finding balance. Remember, algae grows more quickly and more efficiently than your aquarium plants. So if there are more resources than your plants are using, of course it’s going to say, “Thanks very much; I’m going to turn your tank weird colors, now.”

When it comes to nutrients, overdosing with fertilizers can cause algae bloom, so it’s important to be aware of what your plants actually need instead of indiscriminately using ferts in hopes of more plant growth. Aquarium iron supplements are amazing if used properly, but are notorious for this if you use too much. Excess nitrogen/phosphorus can also increase algae, so improperly cycled tanks, overfeeding fish, poor water quality, or messy fish like goldfish that produce a lot of nitrogen-rich waste are potential causes, too. On the flip side, too little CO2 in conjunction with an imbalance in other nutrients or light can cause an algae bloom. 

Good light practices are also essential for algae prevention. Too much light alongside a nutrient imbalance? You're asking for it. Light timers are a must-have and are fairly cheap. If your tank is in direct sun, you're never going to escape algae completely, either. Blue, red, and white lights are the most common on the aquarium market.  Current research suggests white light causes the most algae growth, followed closely by blue lights, and then red. But those lights can also help your plants grow a lot more, so figuring out a balance is key. 

Aquarium Light Timer
An Aquarium Light Timer

Another factor that often gets overlooked is water circulation. Algae loves still or slow-moving water. While stagnant water alone won’t cause algae, it is more likely to form if the water isn’t agitated in some way. Similarly, algae thrives in warmer, shallower environments. Though heat alone won't cause a bloom, if you have a tropical tank, you're more likely to encounter it. 

So, to sum up prevention: do proper water changes, cycle your tank correctly, get a light timer or keep track of how much light your tanks get, fertilize live plants appropriately, and ensure you have good filter flow and tank aeration/water movement. 

Aquarium Air Pump
An Aquarium Air Pump; Good Way to Improve Oxygen/Aeration

Do You Need to Get Rid of Algae?

Maybe. It depends. Generally, a little bit of most species of algae won’t harm your fish or your plants. Some can actually benefit your setup via oxygen production and toxin absorption, but you could just get plants to do that. Seeing some here and there isn’t something to panic over (and you’ll never be able to completely eliminate or prevent it). Planktonic algae in balanced amounts is actually incredibly beneficial in pond environments.

Where you run into problems is when you get too much - of any type. The mat-forming, filamentous species can block out light and gas exchange for fish and underwater plants, which can be fatal. Algae can also coat plant leaves and prevent light from reaching them. And all of them compete with resources with your plants. Beyond all of that? Too much algae can be hideous in an otherwise gorgeous tank. If any of those problems are occuring or look like they're about to occur, that's your sign to treat it more aggressively. 


So, You’ve Decided to Control and/or Get Rid of It. How the Heck Do You Do That?

Once you’ve identified your algae species, there are three main ways to approach control: physical, chemical, and biological.

  1. Physical methods involve manually removing algae. Tools like siphons, scrapers, and sponges for tanks and skimming, dredging, and raking in ponds work well. Light is something to consider, too. You can use a “blackout” method where you limit or completely shut off your lights and block your tank from light to kill it off (if you’re growing plants, they’ll be fine for a few days in a total blackout. Check on them if you’re worried, but a couple of days won’t murder them. Promise). On the other end of the spectrum (pun intended), you can try a UV sterilizer to prevent and control certain algae species. 

    Oh, and pro tip? Don't wash a bunch of algae down your drain after cleaning - several species can clog your pipes. Wouldn't that just be the best reward for finally beating your aquarium algae issue? Calling a plumber? You can seal it in a bag and throw it out. 
  1. “Biological methods” is usually a fancy way of saying “I found something that really, really likes eating this stuff,” but there are other methods as well. Aquatic invertebrates like shrimp and snails can help control algae (Amano shrimp, nerite snails, etc.). Algae-eating fish like plecos, tilapia, mollies, loaches, guppies, corydoras, and Siamese algae eaters are great for eliminating some of your algae. Since these are typically bottom feeders, they'll snack on uneaten food and other materials that, if left alone, can provide algae with resources, too.

    Grass carp can also work in ponds, but only under certain conditions. Those guys require permits/specific genetic statuses in some states, so if you're interested, be sure to look that up for your area. 
    Siamese Algae Eater
    Siamese Algae Eater (Crossocheilus oblongus)
    Fair warning, though: if the fish/invertebrates are herbivorous or omnivorous, they often won't discriminate between eating algae and eating your beloved plants. So keep an eye on them. Also bear in mind that not all of these species will eat every type of algae - several won't even look at cyanobacteria. So don't pick out just any plant-eating fish and get upset if it thinks the algae is gross, too.

    You can also just get more aquarium plants (I know, such a hard decision), which prevent (and treat, to an extent) algae buildup with proper maintenance. Water wisteria (Hygrophila difformis), java moss (Taxiphyllum barbieri), duckweed, and hornwort (Ceratophyllum) are fantastic at algae control because they grow and use resources well. Duckweed is invasive in some areas, though, so check your ag laws before you accidentally choke out an ecosystem by trying to keep algae from choking out an ecosystem. 
A bunch of water wisteria, a hardy, green aquarium plant useful in algae control
Water wisteria, an easy aquarium plant that can help with algae growth

For another type of biological control, you can try microbial algae cleaners, but more research is needed on how good these actually are. Looking out for your existing beneficial bacteria helps enormously with algae control, too. 
  1. Finally, there are several chemical methods that inhibit algae growth or kill existing algae. It’s tempting to jump straight to this option for a quick fix, but we’d recommend exploring other methods in this article first or at least in conjunction with chemical control. These usually have a pretty slim margin of error and I'm too bad at math and anxious about my tanks for that. Personally, I don't like dumping things into my water unless I've tried everything else, but everyone manages their tanks differently (and sometimes, the algae has gotten so out of control there isn't another option). 

    If you do decide to go the chemical route, it's important to be as specific as you can with your treatment: make sure it's safe for your fish, works at your particular water chemistry, and is proven effective for the species of algae you're dealing with. Some algaecides (chemical that kills/prevents algae growth) only work at a particular pH or alkalinity, for example. Also, bear in mind when you're choosing your chemical treatment that "organic" doesn't automatically mean "safer" or "more effective and natural." You know what else is technically organic and natural? Being attacked by a bear. 

    Read labels, warnings, and safety sheets, and dose accordingly. You can find these online fairly easily for whatever product you're using. Calculate the dose you need carefully (do some...algae-bra). Putting more of a chemical treatment than recommended into your setup isn't going to be more effective even if it is satisfying to feel like you're demolishing a stubborn algae's world. That's a waste of money and resources, and can actually be counterproductive in some cases. Similarly, using more than one algaecide can sometimes lead to reduced effectiveness, as well. 

    Chemicals work quickly, which seems like a perfect strategy, but used improperly they can be environmentally damaging/harmful to wildlife, hurt your fish, significantly alter your water chemistry, and can also cause a sharp decrease in oxygen because of the sudden change/algae decomposition. So if you're deadset on using chemicals? Amp up your oxygen/aeration. 

    Something else to take into account are legal factors. If you're treating a pond, it's crucial to have the right permits and approved treatments for your area and know what you're doing. Some chemicals are restricted use. Read up on EPA and USDA guidelines and consider talking to an extension office in your area if you need more information. Additionally, if you have extra chemical treatment you aren't planning to use, you have to dispose of it properly, especially if it's potentially harmful to wildlife. How you do that will depend on your area, but many cities have disposal days where you can bring in hazardous materials and they'll take care of them for you. 

    Chemical methods for algae by species: 
    *some of these are only labeled for use in ponds, and some CANNOT be used safely with fish or aquarium plants or in certain water chemistry, so read your labels, do your homework, and follow instructions
    -Cyanobacteria: copper sulfate, chelated copper, dyes (Aquashade, etc.), diluted hydrogen peroxide, diluted bleach
    -Planktonic: copper sulfate, chleated copper, endothall, sodium carbonate peroxyhydrate, Algaefix, diluted hydrogen peroxide, diluted bleach
    -Filamentous: copper sulfate, chelated copper, dyes, endothall, flumioxazin, sometimes sodium carbonate peroxyhydrate, Algaefix, diluted hydrogen peroxide, diluted bleach
    -Microalgae: copper sulfate, chelated copper, endothall, diluted hydrogen peroxide, diluted bleach

    As you can see, copper products are the gold standard for whatever algae you're dealing with (usually pretty cheap, too) but won't work in all setups. Two other chemical methods that get talked about a lot are antibiotics for cyanobacteria and barley. Given that blue-green algae is bacterial, yes, antibiotics can kill an aquarium outbreak. But that can also kill beneficial bacteria you need for a healthy tank, so wouldn't recommend it as a first option. If you'd like to nuke everything and start over, bleach would probably be cheaper. 

    Barley straw and barley extract, meanwhile, can be added to ponds to prevent algae growth, but this has mixed effectiveness depending on when you apply and your particular setup. May be worth a shot, though. 

All of these methods are viable options, but you should still investigate the cause of the algae outbreak (where the nutrient/light/CO2 imbalance is) and fix it if you can. It's the best long-term solution. Also, just accept the fact that you could be the ultimate, most perfect aquarium person on earth and you'll still get algae. That's the name of the game. 

Since algae is such a common problem for aquarists, Dustin did a bunch of great videos on it. Give them a look if algae is giving you trouble (or if you want to see him use an aquarium siphon as a resistance band):

How to Beat Aquarium Algae (Tips)

How to Treat Cyanobacteria


Algae Controlling Tips. Siamensis Algae Eater, Species Sunday

How to DESTROY Algae in Your Planted Tank

How to Avoid Algae With New Lights in Your Aquarium

Aquarium Algae Tips, Causes of Algae in Greenhouse Sunlight Tanks

How to Beat and Control Black Beard Algae in Planted Tanks: Controlling Algae

As always, hit us with your blog ideas and questions, and tank on!

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