Let’s talk about algae, you know, the green or brown stuff that makes your pretty tank ugly.
The positive side of algae is that its arrival means you have created livable conditions for an organism. Congrats!
The negative side is that it looks unsightly and may harm your aquarium plants.
Before we get into algae control methods, let’s explore some causes of algae in fish tanks.
What Causes Algae in Fish Tanks?
Algae is naturally occurring in almost every water source, even your tap water, so don’t feel blame yourself for the green mess in your tank, blame your neighbor (just kidding, blame nature).
And the main reason you have algae in your aquarium is that you created a great place for it to live.
That means your water supports life. Congrats!
Completely eliminating algae should not be the goal because that would mean your tank is unlivable for other creatures as well.
But controlling algae to the point where you don’t notice its existence is completely doable, even without chemicals.
Why Algae Appears in Fish Tanks
1) Tap water with lots of nutrients and minerals
If your tap water contains high amounts of phosphate, iron, or nitrate, then algae is going to thrive. If possible, consider using water from a source that does not contain these algae fueling nutrients.
2) Too Much Light
Algae likes a lot of light. If you are keeping your aquarium light on constantly, you may be helping algae out compete your plants for nutrients.
Sunlight also seems to cause algae blooms.
If your aquarium is positioned near a window that gets natural sunlight, you may want to find a darker location for it.
Natural sunlight often creates what aquarists call “green water,” , which is actually healthy for your fish and invertebrates but makes your tank look like a disaster.
If you are concerned that reducing light will harm your aquarium plants, don’t worry, aquarium plants only need about 6 to 8 hours of light for photosynthesis.
Consider buying a timer for your aquarium light and don’t let algae see the light of day (pun intended).
3) Overfeeding Your Fish
Fish food contains nutrients like phosphates and iron so excess or uneaten food provides algae with nutrients.
Removing uneaten fish food and performing a water change after a heavy feeding will help prevent algae from proliferating.
Types of Freshwater Aquarium Algae
Before you start your crusade against algae, you should know that there are quite a few different types of algae and even some organisms that look like algae but are, in fact, bacteria.
1) Blue Green Algae or Cyanobacteria
This brownish green blob often hangs out on the substrate. While it looks like a mass of slimy algae, it is in fact a colony of bacteria that have the ability to photosynthesize.
Blue green algae is often smelly but can easily be removed by scraping it off glass and removing bigger chunks with tweezers.
2) Brown Algae
In freshwater tanks, what we call brown algae is actually a diatom. These brownish diatoms usually appear in force between the first and third week of a newly setup tank.
Brown algae will coat everything in slimy brownish layers of film.
Plant leaves, substrate, heaters, filters, and every inch of aquarium glass may turn brown in smaller tanks.
At this point a new aquarist might think, “it’s over,” but there is no need to despair.
Brown algae thrives on silicon dioxide, and other nutrients, and pretty much has those to itself in the first few weeks of a new tank.
But, other species of algae will begin to establish themselves after the third week and compete with the brown algae for nutrients.
The result is that the brown algae will die back and your tank will look great again.
Adding snails and aquarium plants will also help speed up brown algae’s retreat.
3) Green Thread Algae
Green thread algae looks like wispy threads hanging from the top of aquarium plants.
Removing may only require moving your finger or a pair of tweezers in a circular motion over the algae and then pulling it up and out of the tank.
4) Green Hair Algae
Green hair algae can appear quickly and may cover plants with it’s spikey looking filaments.
Removing green hair algae by hand is a challenge but can be done.
Aquarium Snails and aquarium shrimp like Amano shrimp may help limit the spread of the green hair algae and will eat other types of algae as well.
Plus, if you have not tried keeping freshwater shrimp like Cherry shrimp, you are missing out, they are a lot of fun to watch.
5) Staghorn Algae
Staghorn algae looks like a big chunk of hair.
Not to be confused with green hair algae, Staghorn algae is a pale grey is color and tends to attack itself to aquarium décor, equipment, and slow growing plants like Java fern.
6) Green Spot Algae
Green spot algae appear as crusty green spots on aquarium glass and plants leaves.
Green spot algae tends to thrive under strong lighting so reducing the amount of hours your light is on may help with long term control.
Removing it from aquarium glass may require a razor blade.
If the algae are on a plant leaf, you may want to simply remove that leaf but scraping it off with a toothbrush may work.
7) Black Beard (or Brush) Algae
As you might have guessed from its name, this algae forms a dense mat of filaments that look like a brush or a beard.
Like Staghorn algae, black beard algae grows on aquarium decorations, rocks, plants, and substrate.
Black beard algae holds on tight, so removing it with your finger or a toothbrush is challenging.
If practical, you may want to remove the item that the algae is growing on and give it a hydrogen peroxide bath, followed by a rinse in regular water to remove the algae.
8) Green Water
Green water is usually caused by tiny free floating algae in the genus Chlorella.
Tanks that are near windows that get natural sun light may experience Chlorella blooms because the algae seems especially attuned to sunlight.
Some aquarists actually try to create green water because it is thought to have health benefits for certain organisms like shrimp and even sick fish.
If you want some detailed pictures to help you identify which algae is in your aquarium, check out Aquasabi’s article on algae.
Aquarium Algae Control
Controlling algae and removing algae are slightly different goals, and this article will talk about both.
You can think of controlling algae as the war, while removing algae is the immediate battle.
There will be some overlap between the two, but focusing on algae control rather than immediate removal will lead to long-term success.
Algae Control Tips
1) Test Your Water
I know testing your water feels like a chore, but it can be really easy if you buy the aquarium water test strips only need to be dipped into the tank water for a couple seconds.
Yes, a complete aquarium water testing kit is more accurate but the test strips are more than adequate for figuring out if your water is loaded with nitrates.
Algae thrives off excess nutrients, and high levels of nitrates may be helping the algae spread quickly.
2) Increase Frequency of Water Changes
In natural ponds and lakes, rainwater refreshes aquatic environments by diluting and carrying away chemicals and nutrients like nitrates.
In a fish tank, that becomes your job.
Increasing how often you perform water changes will decrease nitrates and organic compounds, both of which fuel the growth of algae.
Also, if you feed your fish frequently or heavily, performing additional water changes will help keep your water at normal nutrient levels.
3) Add Plants or Add More Plants
Adding aquarium plants helps control algae because plants release chemicals that inhibit the growth of algae; it’s the way plants compete.
However, if excess nutrients or excess light are present, algae will typically get the upper hand over plants and cover the plants to the point that the plants cannot photosynthesize and die.
But, if nutrients and light are in limited supply, plants will typically outcompete algae because they are able to store nutrients more efficiently.
If you need plants that can grow in low light conditions, get some Java Ferns and some Java moss; both will help you fight against algae.
4) Stock Your Tank with Algae Eaters
Fish like Otocinclus and Bristlenosed plecos devour algae.
If your tank is small, stick with an Otocinclus or four because plecos tend to get pretty big.
Snails and Freshwater Aquarium shrimp, like Amano shrimp, are excellent algae eaters. In fact, only snails and cherry shrimp clean one of my tanks and it looks great!
5) Reduce Light
If your aquarium does not have live plants, reducing how long your light is on will help prevent algae growth.
If you leave your aquarium light on for 10 hours, try leaving it on for 4 to 5 hours.
If you have a planted tank, 6 to 8 hours of light a day is ideal for plants; any more than that and algae will begin to gain a photosynthetic advantage over the plants.
Ways to Remove Aquarium Algae from Plants and Décor
Starting with my least favorite method and ending with my most preferred way to remove algae:
5) 5% bleach solution (1 part bleach to 19 parts water): Hold or dip algae infested plant into the solution for 30 seconds (make sure to wear protection!).
Then rise plants in regular water. Make sure not to dip the plant roots in the solution, only the infected leaves.
This method works best for black beard algae, which is hard to kill unless removed by hand or with this method.
Is this method safe for fish? NO, be extra careful before bleach dipped plants back into a fish tank, it is safer to quarantine the plants in a separate tank for a few days and let the chemical residue break down before adding the plants back to your aquarium.
I do not personally use the bleach dip method to remove algae from my plants because I prefer not to deal with something as toxic as bleach.
Also, bleach is corrosive, so if it gets on anything, clothes, carpet, etc., it’s pretty much ruined. But here’s a video of how it’s done:
4) 3% Hydrogen Peroxide: Spray algae infected area with hydrogen peroxide.
Works best for black beard algae because that algae is hard to eliminate.
Safe for Fish? NO, again, similar precautions should be taken for hydrogen dipped plants as for bleach dipped plants.
I have seen videos of people spraying Hydrogen Peroxide directly into their aquarium.
I would do that, but I want my fish to live.
Instead, just remove the plant you want to treat and dip it into a Hydrogen peroxide bath.
Then rinse off the plant.
I also do not personally use this method but at least peroxide is not as toxic as bleach.
But, if you want to try using hydrogen peroxide in your tank to remove algae, check out the video.
3) Scrub it away
The good old elbow grease method. Grab a toothbrush, sponge, or those fancy magnets and get to work scrubbing that glass.
You can use your hands and fingers to remove algae from plant leaves.
Safe for fish? Yes, unless you are a maniac.
2) Get some Amano Shrimp
Amano shrimp are voracious algae eaters and will help you battle algae problems over the long term.
These shrimp are not an instant solution, but they will eat algae and they are fun to watch.
Other freshwater shrimp species like cherry shrimp will also eat algae, but I find that Amano shrimp work a little harder to find algae.
1) Use Snails
I discovered this secret weapon by accident.
People probably don’t mention snails because they are treated like the plague.
But, I bought some new aquarium plants and (of course) after a couple weeks my entire tank was covered in algae, the long stringy type.
I mean my plants were covered in stringy green stuff and the foreground looked was covered in a fluffy shag carpet.
I also noticed baby snails in my tank.
I then drained my tank and threw it in a dumpster.
Just kidding! I actually just left it alone and to my amazement, my jaw dropped, the tank was spotless after about a week.
As soon as the snail army gained enough recruits, they demolished my algae problem.
Yes, not I have a snail problem, but I prefer that to an algae problem.
Seriously, get a couple Ramshorn or Nerite snails if you need to rid yourself of algae and keep it that way.
Snails are a safe, effective, and relatively quick solution for removing algae.
Snails will leave most of your plants alone too, but I have noticed that my Staurogyne repens is a little chewed up.
But, the snails have not touched my Java ferns or Anubias plants.
The main takeaway about aquarium algae is shifting from an “eliminate it” mindset to a “control” or maintain it mindset.
Algae is a natural part of having an aquarium and it should not decrease the enjoyment of your tank.
Setting up systems for controlling algae, like increasing water changes and adding snails, is all part of the joys of maintaining a beautiful tank.
If you let yourself enjoy the process of aquarium maintenance, even scrubbing algae can be relaxing.
Stay zen aquarists.