Health and troubleTM-17
Aquarium Algae Control: Telling Brown, Green, Black Beard and Blue-Green Algae Apart, Their Causes, and Using Light, Water Changes, Algae Eaters and Tools
For aquarium algae control, the fastest path is to identify the algae, cut back light and nutrients, then remove the rest by hand and with algae eaters.
In this article (18 sections)
- In short: where do you start with aquarium algae control?
- What kind of organism is aquarium algae?
- Why does algae grow in an aquarium?
- How should you change the lighting to control aquarium algae?
- What water changes and cleaning help control aquarium algae?
- How do you reduce brown algae and green algae?
- How do you reduce black beard algae?
- How do you reduce blue-green algae?
- How do you clear green water?
- Which algae eaters should you choose?
- What should you watch for when adding algae eaters?
- What tools do you use to clean algae in an aquarium?
- Is it OK to use an algae inhibitor?
- What are common mistakes in aquarium algae control?
- What terms come up in aquarium algae control?
- What else goes with aquarium algae control?
What are common questions about aquarium algae control?6
- Sources
In short: where do you start with aquarium algae control?
Start aquarium algae control by identifying which algae you have. Next, cut back light and nutrients, then remove what is left with tools and algae eaters.
Algae grows in any tank that has light and nutrients in the water. Manufacturers' guides also recommend learning to live with algae rather than trying to get rid of it completely.
The trouble is that what works depends on the type of algae. An animal that eats brown algae will barely touch black beard algae.
What this article covers:
- How to tell brown algae, green algae, black beard algae, blue-green algae and green water apart
- Why algae grows, and how to adjust lighting and water changes
- How to remove each type of algae
- Which algae the otocinclus, Amano shrimp, nerite snail and others eat
- Cleaning tools, and common mistakes
First, a quick reference for this page. Tell aquarium algae apart by color, location and when it appears.
| Algae | Color and shape | Where it tends to grow | When it appears, and cause |
|---|---|---|---|
| Brown algae (diatoms) | Brown. Spreads thinly and is soft | Glass, substrate, rocks, driftwood | Soon after setting up the tank |
| Green algae | Bright green. Comes as spots, films or threads | Glass, rocks, driftwood, plants | A while after setup. Too much fertilizer |
| Black beard algae (red algae) | Black, gray or dark green. Grows in tufts and holds on firmly | Leaf edges of plants, driftwood, equipment | Tanks that have run a long time. Too few water changes or too little cleaning |
| Blue-green algae | Dark green film. Has a musty smell | Surface of the substrate, spots where water stagnates | Any time. Lots of leftover food or waste |
| Green water | The whole tank turns cloudy green | The water itself | Tiny algae multiply in the water |
The key point: in aquarium algae control, identifying the type before choosing a fix saves wasted effort.
What kind of organism is aquarium algae?
Most aquarium algae are true algae. Blue-green algae is the exception: it is not an alga but a type of bacteria that photosynthesizes.
Kamihata's guide divides aquarium algae into four broad groups. Each group catches light with different pigments, so the guide says the color of the lighting also changes how easily each one grows.
| Group | Typical algae | Features |
|---|---|---|
| Diatoms | Brown algae | Has a glassy shell. Soft, and many animals eat it |
| Green algae | Green algae, thread algae, green water | Green like aquarium plants. Comes in many shapes and degrees of hardness |
| Red algae | Black beard algae | Holds on firmly, and few animals eat it |
| Blue-green algae | Blue-green algae (cyanobacteria) | Spreads like a film and grows fast |
Algae and plants both grow on light and nutrients. In a tank where plants grow well, expect a little algae too, and you will not panic.
Why does algae grow in an aquarium?
The main cause of aquarium algae is too many nutrients in the water and too much light. GEX's guide names high levels of phosphate and silicate as the main causes.
Here are the causes GEX lists, with what to check for each.
| Cause | What is happening | What to check |
|---|---|---|
| Not enough bacteria | Waste is not fully broken down | Do not rush setup. Do not rinse filter media in tap water |
| Not enough water changes or gravel cleaning | Nutrients build up in the water | Review how often and how much water you change |
| Too much food | Leftover food becomes nutrients | Feed only what they can finish |
| Too many fish | More waste dirties the water | Review water changes before adding more fish |
| Too much plant fertilizer | Fertilizer feeds the algae | Cut back or stop fertilizer for a while |
| Direct sunlight | Light is too strong and lasts too long | Move the tank or block the light |
| Algae spores on tools | Algae is brought in from another tank | Keep separate tools for each tank |
GEX's guide says that even an algae inhibitor will not solve the problem at its root unless you fix the cause. The foundation of aquarium algae control is to go through the right-hand column of the table one item at a time.
How should you change the lighting to control aquarium algae?
The easiest step is to shorten how long the light is on. If you normally run it 8 to 10 hours, cut it to about 6 hours when algae is bad (Kamihata).
Look at both how long the light is on and how bright it is. These are the lighting adjustments in Kamihata's guide.
| Adjustment | What to do | When it fits |
|---|---|---|
| Shorten the time | Cut it to about 6 hours for a while | When algae suddenly increases |
| Make it dimmer | Raise the light, or soften it with the lid | When algae grows on the leaves of plants that need little light |
| Make it brighter | Give plants enough light | When plants are not growing and algae is winning |
| Block the light | Keep the tank completely dark for about a week | Works on some types. Plants weaken too |
A tank in a sunny spot will grow algae. Before changing the light, first check whether sunlight from a window reaches the tank.
It may seem surprising that more light can sometimes mean less algae. When plants grow vigorously, they use up the nutrients in the water first.
Put the light on a timer so it comes on for the same hours every day, and it will never be left on by mistake. Once the algae settles down, bring the hours back up little by little.
What water changes and cleaning help control aquarium algae?
Water changes dilute nutrients, and cleaning removes dirt from the substrate and filter. Kamihata's guide says to clean the filter once every 1 to 3 months.
These are the ways to reduce nutrients in the water from Kamihata's guide.
- Dilute built-up nutrients with water changes
- During water changes, siphon out dirt that has collected in the substrate
- Clean the filter once every 1 to 3 months. Rinse the media gently in tank water
- Plant fast-growing plants to soak up nutrients
- Cut back or stop plant fertilizer until the algae settles down
The filter media is home to bacteria that break down waste. Scrubbing it hard in tap water weakens that work too.
Kamihata's guide names fast-growing plants such as hornwort and anacharis. In a tank with only slow-growing plants, adding fast growers makes algae less likely.
The amount of food matters as much as water changes. Leftover food turns straight into nutrients and feeds the algae.
How do you reduce brown algae and green algae?
On glass, scrub off brown and green algae with a sponge or scraper. When there is a lot, combine algae eaters with water changes.
Brown algae often appears in newly set up tanks. Kamihata's guide says it often fades on its own once the tank settles.
| Brown algae | Green algae | |
|---|---|---|
| When it appears | Soon after setup | A while after setup |
| Tools for removing it by hand | Sponge or scraper for glass. Brush for rocks and driftwood | Same |
| Animals that eat it on glass and rocks | Otocinclus, bristlenose pleco, nerite snail | Same. Nerite snails eat only the soft kinds |
| Animals that eat it on plants and equipment | Amano shrimp, Neocaridina shrimp | Same. Neocaridina eat only the soft kinds |
| Other steps | Shorten the light hours for a while | Reduce nutrients with water changes |
Some green algae sticks hard as spots, and some grows out in threads. Few animals eat hard green algae, so tools are faster.
Thread algae tangled in plants cannot be fully removed by hand. Kamihata's guide recommends picking it out with tweezers and using Amano shrimp for the tougher kinds.
How do you reduce black beard algae?
Reduce black beard algae by removing it by hand, cutting off affected leaves and doing more water changes. Few animals eat it, so the trick is not to rely on animals alone.
Black beard algae tends to appear in tanks that have run for a long time. Kamihata's guide names too few water changes and too little filter cleaning as causes.
Steps to reduce black beard algae:
- Cut off the old affected leaves of plants with scissors
- Take out removable rocks, driftwood and equipment and scrub them with a brush
- Do more water changes and stop fertilizer for a while
- For whatever remains, use a commercial algae inhibitor according to its instructions
Kamihata's guide also mentions soaking removed items in boiling water. Use boiling water only outside the tank, and only on items with no animals on them.
GEX and Kamihata both name the Siamese algae eater (サイアミーズ・フライングフォックス) as a fish that eats black beard algae. It is not yet in this site's compatibility data.
The easiest way to deal with black beard algae is to cut off the leaf the same day you spot it. Once it spreads, removing it takes many times the effort.
How do you reduce blue-green algae?
Reduce blue-green algae by siphoning it out and creating water flow where the water stagnates. It grows fast, so remove it and cut back the cause at the same time.
Blue-green algae spreads like a dark green film and has a musty smell. Kamihata's guide says it tends to appear where dead leaves, leftover food and waste collect.
| Fixes for blue-green algae | What to do |
|---|---|
| Remove it | Siphon it out with a hose or pipette. Scoop it up with a fine net |
| Reduce nutrients | Change water more often. Remove dead leaves |
| Get rid of stagnant spots | Turn the filter outlet to create water flow |
| Use an inhibitor | Follow the instructions, and check that it is safe with shrimp and plants in the tank |
Few animals eat blue-green algae. Kamihata's guide names the Amano shrimp as one candidate.
If stagnant spots remain after you remove blue-green algae, it comes right back. Changing the water flow is part of the job.
How do you clear green water?
Green water is a bloom of tiny algae floating in the water. Water changes tend to clear it only for a few days, and Kamihata's guide says a UV sterilizer works well.
A UV sterilizer shines ultraviolet light on the water to reduce floating algae and bacteria. It cannot remove algae already growing on glass or rocks.
Green water is sometimes welcome when keeping medaka or goldfish outdoors. In an indoor tank the problem is how it looks, so check the light hours and sunlight first.
Which algae eaters should you choose?
Choose algae eaters by the type of algae in your tank. GEX's guide says each animal eats different algae, so it is best to combine them.
Based on GEX's and Kamihata's guides, here is what the animals covered on this site eat.
| Animal | Algae it eats well | Algae it avoids, and cautions |
|---|---|---|
| Otocinclus | Brown algae, soft green algae | Does not eat black beard algae. Algae alone is often not enough food |
| Amano shrimp | Thread algae, algae on fine leaves and substrate | Gets eaten by fish with big mouths |
| Neocaridina shrimp | Soft algae, algae on plants | Not good with hard algae |
| Nerite snail | Brown and green algae on glass, rocks and driftwood | Not good with hard green algae. Lays white eggs on the glass |
| Bristlenose pleco | Algae on glass, rocks and driftwood | Holds territory against its own kind |
If you are unsure, GEX's guide recommends the otocinclus and the Amano shrimp together. Adding one glass grazer and one plant grazer means less algae gets missed.
Here is how these five get along with each other, from this site's calculation.
| 1 | 2 | 3 | 4 | 5 | |
|---|---|---|---|---|---|
| 1Otocinclus | · | ○ | △ | ○ | ○ |
| 2Amano shrimp | ○ | · | ○ | ○ | ○ |
| 3Japanese swamp shrimp | △ | ○ | · | ○ | ○ |
| 4Nerite snail | ○ | ○ | ○ | · | ○ |
| 5Bristlenose pleco | ○ | ○ | ○ | ○ | · |
○ Generally compatible △ With care × Not recommended
Source: Judged by this site's rules from the care data of each species (see the sources of the care data table)
There is only one △: the otocinclus and the Neocaridina shrimp. The otocinclus may pick at baby shrimp, but adult shrimp are left alone.
What should you watch for when adding algae eaters?
Before adding algae eaters, think about compatibility with your current fish and what they will eat once the algae is gone. If you assume they can live on algae alone, they may grow thin.
Water temperature and size differ from animal to animal. Here they are side by side.
| Species | Adult size (cm) | Temperature (°C) | pH | Swimming level |
|---|---|---|---|---|
| Otocinclus | 3.5 | 21–26 | 5.5–7.5 | Bottom |
| Bristlenose pleco | 12.5 | 21–26 | 5.5–7.5 | Bottom |
| Japanese swamp shrimp | 2.8 | 23–28 | 6.5–7 | Bottom |
| Amano shrimp | 4 | 20–28 | 6.5–7.5 | Bottom |
| Nerite snail | 2 | 10–28 | 7 |
Source (5)
- Seriously Fish (Otocinclus macrospilus)
- Seriously Fish (Ancistrus cf. cirrhosus)
- GEX (temperature), Tokyo Aqua Garden (pH, level, temperament), Kyoto Prefecture Red Data Book 2015 (size)
- GEX (temperature), Tokyo Aqua Garden (pH, level), Hyogo Prefecture Red Data Book (size)
- Tokyo Aqua Garden (temperature, pH, temperament), Ishikawa Prefecture Red Data Book (size)
An algae eater is no use if your current fish eat it. With goldfish, for example, the nerite snail is ○, but the Amano shrimp and the otocinclus are ×.
| What to watch | What happens | What to do first |
|---|---|---|
| Compatibility with current fish | Gets eaten or chased | Pick two species in the checker below and check |
| Food after the algae is gone | Otocinclus and others grow thin | Add sinking food or vegetables |
| Adding too many | They eat all the algae and run short of food | Start with a few, and add more as you watch the algae go down |
| Amano shrimp escaping | They climb out through gaps in the lid | Close the gaps in the lid |
The detailed reasons behind each match are in Otocinclus Tank Mates and Shrimp Tank Mates. Before choosing an algae eater, check the ○△× with your current fish once, and you can add it with peace of mind.
Think of algae eaters as the crew that keeps algae from spreading. If you expect them to wipe out every bit of algae that has grown, you will be disappointed.
What tools do you use to clean algae in an aquarium?
Use different tools for different places in the tank. Kamihata's guide says it helps to have a scraper, a sponge, tweezers and similar tools on hand.
| Tool | Where it works | Algae it suits |
|---|---|---|
| Scraper (a blade for glass) | Glass | Brown algae, green algae, hard spot algae |
| Melamine sponge | Glass | Brown algae, soft green algae |
| Brush | Rocks, driftwood, equipment | Brown algae, green algae, black beard algae |
| Pipette, hose | Substrate, gaps between plants | Blue-green algae, bits of scraped-off algae |
| Tweezers, scissors | Plants | Thread algae, leaves with black beard algae |
| Fine net | Surface and midwater | Floating algae, blue-green algae |
Acrylic tanks scratch more easily than glass. Check the tool's instructions to make sure it is safe for acrylic before you use it.
Scraped-off algae left in the water turns back into nutrients. Siphon it out with a water change right after scrubbing, and the job is done in one go.
Is it OK to use an algae inhibitor?
An algae inhibitor can help when algae is bad. But manufacturers' guides also say it will not solve the problem at its root unless you fix the cause.
Some algae inhibitors work by taking up the nutrients algae needs, and some act on the algae directly. Before using one, check these points in the instructions.
- Whether it is safe in a tank with shrimp or snails
- Whether it is safe for plants close to algae (such as willow moss)
- The dose, and how many days in a row to use it
An inhibitor is something to add after you have fixed the lighting and water changes. If you use it first, the algae grows back when you stop.
What are common mistakes in aquarium algae control?
There are three common mistakes in aquarium algae control. They are relying too much on animals, leaving the light on, and panicking over brown algae right after setup.
| Common mistake | What happens | What to do instead |
|---|---|---|
| Relying only on algae eaters | Algae they avoid is left. They grow thin once they eat it all | Fix the cause and combine them with tools |
| Leaving the light on for long hours | Too much light, so algae increases | Set the hours with a timer |
| Panicking over brown algae right after setup | You rush to add animals or chemicals | It often fades once the tank settles. Scrub it off and wait |
| Scrubbing filter media hard in tap water | The breakdown of waste slows | Rinse it gently in tank water |
| Feeding a little too much | Leftover food feeds the algae | Feed only what they can finish |
| Leaving black beard algae alone | It spreads and gets harder to remove | Cut off the leaf as soon as you spot it |
When algae increases, think back to the last thing you changed, and you will find the cause faster. It is often one of these: you added fish, you added more fertilizer, or you changed the light.
What terms come up in aquarium algae control?
| Term | Meaning |
|---|---|
| Diatoms (珪藻) | Algae with a glassy shell. The source of brown algae |
| Green algae (緑藻) | Algae green like aquarium plants. The source of green algae and green water |
| Red algae (紅藻) | The group black beard algae belongs to. Holds on firmly and is hard to remove |
| Blue-green algae (藍藻) | A type of bacteria that photosynthesizes. Spreads like a film |
| Green water (青水) | Water turned cloudy green by a bloom of tiny algae |
| Filter media (ろ材) | The material inside the filter. Home to bacteria that break down waste |
| Cycling a new tank (立ち上げ) | Filling a new tank and getting it ready for animals to live in |
| Algae inhibitor (コケ抑制剤) | A commercial product that keeps algae from increasing |
| UV sterilizer (紫外線殺菌灯) | A device that shines ultraviolet light on water to reduce floating algae and bacteria |
What else goes with aquarium algae control?
Aquarium algae control is tied to the compatibility of algae eaters. Go on to the article for the animal you want to add.
- Otocinclus compatibility and food: Otocinclus Tank Mates
- Amano shrimp and Neocaridina shrimp compatibility: Shrimp Tank Mates
- Algae eaters for a medaka tank: Medaka Tank Mates
- Algae eaters for a goldfish tank: Goldfish Tank Mates
Tank mates by speciesOtocinclus Tank Mates: 22 Species Rated ○△× with Reasons, Why They Get Bullied, Medaka, Goldfish, Shrimp, Algae and FoodOtocinclus tank mates for 22 species rated ○△× with reasons. Why otos get bullied, × bettas, angels and goldfish, △ medaka and shrimp, algae, food and numbers.
Shrimp and snailsWhich Fish Can Live with Shrimp? Neocaridina and Amano Ratings, Hiding Places, AcclimationShrimp tank mates rated ○△× with reasons for Neocaridina and Amano shrimp. Fish that eat baby shrimp vs adults, willow moss hiding places and acclimation steps.
Tank mates by speciesMedaka Tank Mates: 22 Species Rated ○△× with Reasons, plus Tropical Fish, Shrimp, Nerite Snails, Goldfish and No HeaterMedaka tank mates for 22 species, rated ○△× with reasons. Three shrimp and the nerite snail are ○. Why tropical fish are △ or ×, goldfish, and outdoor ponds.Tank mates by speciesGoldfish Tank Mates: 22 Species Rated ○△× with Reasons, plus Tropical Fish, Shrimp, Medaka, Cleaners and Goldfish VarietiesGoldfish tank mates for 22 species, rated ○△× with reasons. Why small fish and shrimp are ×, why tropical fish are △, medaka, nerite snails and tank size.What are common questions about aquarium algae control?
Is there a way to stop algae from growing in an aquarium?
There is no way to get rid of algae completely. Any tank with light and nutrients grows at least a little.
To reduce it, set fixed light hours and dilute built-up nutrients with water changes. Scrubbing it off early keeps it from spreading.
Why is my aquarium covered in algae?
Too much light and too many nutrients are the main cause. Direct sunlight, too much food, too few water changes and too much fertilizer often add up.
Thinking back to the last thing you changed helps you narrow down the cause.
Can I leave algae in my aquarium alone?
Brown algae in a newly set up tank often fades once the tank settles. Black beard algae and blue-green algae spread if left alone.
Remove black beard algae and blue-green algae early, as soon as you spot them.
What is the best animal for eating algae?
No single animal eats every kind of algae. On glass, otocinclus and nerite snails suit; on plants, Amano shrimp suit.
Check compatibility with your current fish before choosing.
What is good for algae in a goldfish or medaka tank?
In this site's calculation, the nerite snail is ○ with both goldfish and medaka. The Amano shrimp is ○ with medaka and × with goldfish.
For a goldfish tank, nerite snails suit better than shrimp.
Does anything eat black beard algae?
GEX's and Kamihata's guides name the Siamese algae eater. Most algae eaters will not eat black beard algae once it has grown.
Cutting off the leaf is the sure way to deal with black beard algae.
Sources
- Kamihata: Causes and fixes for each type of algae in aquarium tanks (アクアリウム水槽に発生する苔（コケ）の種類ごとの原因と対策, in Japanese. The four groups of algae and their pigments, when and where each type appears, lights on 8 to 10 hours or about 6 hours when algae is bad, blocking light, cleaning the filter once every 1 to 3 months, fast-growing plants, stopping fertilizer, tools for removing algae by hand, algae eaters, boiling water, green water and UV sterilizers)
- GEX: The best algae eaters for tropical fish, by type of algae (【コケ種類別】熱帯魚飼育におすすめのコケ取り名人, in Japanese. The four groups of algae, each animal eats different algae, the otocinclus and Amano shrimp pair, fish that eat black beard algae, phosphate and silicate as the main causes, seven causes)
- Aquarium Co-Op: Otocinclus Catfish (eats soft algae and diatoms and avoids hard algae, running short of food, too many will eat all the algae)
- Tokyo Aqua Garden: How to keep otocinclus (オトシンクルスの飼育方法, in Japanese. Eats brown algae, does not eat black beard algae or blue-green algae)
- Tokyo Aqua Garden: Amano shrimp (ヤマトヌマエビ, in Japanese. Eats algae, gets attacked by angelfish)
- Tokyo Aqua Garden: Nerite snail (石巻貝, in Japanese. Eats algae and leftover food, lays eggs on the tank walls, does not multiply in the tank)
- Aquarium Co-Op: Amano Shrimp (watch out for escapes)
- Seriously Fish: Ancistrus cf. cirrhosus (the bristlenose pleco holds territory against its own kind and similar-shaped fish)