Is Algae Bad For An Aquarium?

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No matter what size tank you have, no matter what equipment you use, no matter how long you have been in the hobby, algae is a constant foe, if not causing you grief right now, then waiting in the background to strike!

Ok, so that is a little dramatic, but algae is a constant problem for many of us, and even after keeping fish for over 30 years, and even with a fish room full of tanks, I still haven’t managed to defeat my arch enemy, algae.

What is Algae?

According to Wikipedia, algae is…

an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular microalgae, such as Chlorella, Prototheca, and the diatoms, to multicellular forms, such as the giant kelp, a large brown alga that may grow up to 50 meters (160 ft) in length.

To those of us without a biology degree, algae is a simple plant life form that can quickly cover multiple surfaces in our aquariums. Algae can be green, brown, or black and can lay flat on a surface, like green spot algae, or form long strands, as in the case of hair or black beard algae.

Some types of algae, like brown diatom algae, are notorious for growing in new tanks, whereas some of the hair-like algae, such as Black Beard Algae, usually develop in more mature tanks.

Is Algae Bad?

Controversially, I don’t believe algae is bad. In fact, I actively encourage algae to grow in many of my tanks, although I really only want it to grow where I want it to grow.

If we think of algae in terms of a plant, it is beneficial in that it absorbs fish waste. Algae can help reduce nitrates in our aquariums.

Much like plants, algae produce oxygen during the day and carbon dioxide at night. However, unlike plants, algae doesn’t need a complex set of nutrients to be able to grow. In fact, algae can often take advantage of a single nutrient being present in the aquarium water.

It is precisely because algae doesn’t need a full range of nutrients to grow, that it can easily take over a tank, especially a tank where water conditions are less than favorable.

Algae also does not need a full spectrum of light like plants do, meaning algae can take advantage of poor lighting and grow where few plants would.

Having algae growing in our tanks can help ‘soften’ the edges and make our tanks look more natural. In my opinion, a rock or piece of wood that has some algae growing on it looks much more natural than one which is shiny and new and looks like you brought it home from the store.

What Causes Algae?

Essentially, the cause of algae in an aquarium is the imbalance of light and nutrients.

As mentioned above, plants need just the right balance of light and nutrients to be able to thrive, whereas algae can take advantage of whatever light and/or nutrients are available.

Providing too much light and not enough nutrients will cause an aquarium to be out of balance, as will adding too many nutrients and not providing enough light

Once you realize the secret to minimal algae is balancing light and nutrients, you open yourself up to the prospect that an aquarium can never be in perfect balance as plants are continually growing, dying, and being trimmed, meaning the number of nutrients being required today will almost certainly be different to the amount required in 3 months time when the plants have grown!

What Different Types of Algae Are In Aquariums?

In my experience, there are basically 8 different types of algae we are likely to come across on a regular basis in our freshwater aquariums. These are;

  • Brown Diatom Algae
  • Green Spot Algae
  • Black Beard Algae
  • Green Hair Algae (Thread Algae)
  • Green Water
  • Staghorn Algae
  • Green Dust Algae
  • Blue-Green Algae (cyanobacteria)

Below I look at each of these algae in turn and make some recommendations on removing each one based on my experience of what has worked over the years.

Brown Diatom Algae

Brown Diatom Algae, which can actually also be green in color, is one of the first algae to appear in a newly setup aquarium. The major cause of Brown Diatom Algae is high levels of phosphates and silicates.

Brown Diatom Algae is one of the easiest algae to remove. It is a soft algae that can be wiped away with algae scrubbing sponges like these ones from

There are also plenty of algae-eating fish that will eat Brown Diatom Algae, with Otoclincus probably being the most voracious Brown Diatom Algae eater in the hobby.

In truth, if just left alone, Brown Diatom Algae will usually just go on its own, providing you have at least some plants in the aquarium. This is because aquarium plants are fairly quick to consume both phosphates and silicates, starving the algae out and leading to its disappearance.

Green Spot Algae

In contrast to the relatively easy-to-remove Brown Diatom Algae, Green Spot Algae (sometimes referred to as GSA) can be fairly difficult to remove. It is hard to scrape off and there are few fish in the hobby that will eat it.

Green Spot Algae is made up of tiny, hard green spots which grow on the aquarium glass, equipment, and on slower growing, broad-leaved plants.

Because Green Spot Algae is so tough, there are few fish that will eat it. In fact, I am not sure I know of any fish that will actively choose to eat Green Spot Algae. The most effective way I have found to remove Green Spot Algae is with Nerite Snails.

Nerite Snails are a species of aquatic snail that specializes in eating algae. One of the other major bonuses of Nerite Snails is that they won’t reproduce in our freshwater aquariums. Their offspring have to pass through brackish (meaning slightly salty) water before they become snails, meaning there is no way to go from egg to snail in our tanks.

Nerite Snails

If you have Green Spot Algae, but don’t fancy adding Nerite Snails to your aquarium, try scraping the Green Spot Algae off the glass and equipment using either a blade or a Mag-Float with a blade attachment like this one.

Black Beard Algae

Black Beard Algae is the bane of my fishkeeper’s life. This notoriously difficult to remove algae grows as small black tufts which can appear on anything in the aquarium, including the plants.

Black Beard Algae, which can also be grey, brown, or red, is another tricky algae to irradicate. It forms thick, bushy clumps, often on driftwood, aquarium decorations, or plant leaves. Left untreated it can quickly take over an entire aquarium, ruining the look the fishkeeper was going for and eventually killing any plants that it covers.

There are a number of fish you can add to a tank that will eat Black Bead Algae. Siamese Algae Eaters are probably one of the best known in the hobby, but Florida Flag Fish and Black Mollies will also eat Black Beard Algae, helping to keep it at bay if not remove all traces.

One trick to preventing Black Beard Algae forming, or at least keeping it to a minimum, is adding Amano Shrimp. Amano shrimp are named after the world’s most famous aquascaper, Takeshi Amano. Takeshi Amano used Amano Shrimp in almost all of his aquascapes, making them an instant hit in the fish-keeping world.

Amano Shrimp

There are also chemical treatments available that will help reduce the amount of Black Beard Algae in your tank.

There are a number of liquid carbon products on the market that can be used to treat Black Beard Algae. For a mild outbreak, products like Seachem Excel (see more about Seachem Excel) can be used to treat the entire water column. For more severe cases of Black Beard Algae, the water level can be dropped and the liquid carbon squirted directly on the algae, before refilling the tank.

Caution should be used when adding any chemical to an aquarium, but some plants like Vallisneria are sensitive to liquid carbon and make die when it is added to the tank.

Green Hair Algae

Green Hair Algae, which is sometimes called Thread Algae, has the appearance of long, wet hair, hence the common name.

Green Hair Algae can seemingly appear from nowhere due to the rapid rate at which it can grow. The major cause of Green Hair Algae is too much light in the aquarium. When aquarium lights are left on for 12 or more hours a day, the plants quickly absorb all the available nutrients, leaving the door wide open for Green Hair Algae.

Removal of Green Hair Algae can be tricky. Large clumps can be removed by manually pulling on them or winding a stick around and around in the hair algae, pulling it away from whatever it is growing on.

There are a number of fish that will happily pick at and eat Green Hair Algae. Siamese Algae Eaters and Florida Flag Fish are the most likely candidates to make a real dent in the algae. Amano Shrimp will also eat some Green Hair Algae, although they are definitely better at preventing the algae in the first place.

One of the most effective, although slow, treatments I have found for riding my tanks of Green Hair Algae involves decreasing the amount of light by reducing the hours the light is on whilst simultaneously increasing the number of nutrients I add to the tank.

This technique works by making the plants stronger, allowing them to out-compete the Green Hair Algae.

Green Water

Green Water is the name given to the single-celled algae known as phytoplankton that makes your tank look like a bowl of pea soup.

Phytoplankton is a free-floating form of algae that doesn’t attach itself to any part of the aquarium, it literally just floats around and multiplies. The algae causing Green Water multiplies at such a quick rate, that even by water changing the aquarium water every day, the Green Water will return the first day you stop changing water.

Whilst there are some fish babies that will actively eat the free-floating algae, clearly, they will never be in your tank in large enough quantities to even make a dent.

There are only two ways I know of to get rid of Green Water and they are either totally blacking out your tank for 7 to 10 days or using a UV sterilizer.

Blacking out a tank

Blacking out a tank means exactly that. You need to turn off the light over your aquarium, then cover the entire tank with something large enough and thick enough that no light can pass through it.

If even the smallest amount of light can get through, the floating algae will continue to duplicate.

After 7 to 10 days the algae should have all died and the water should be clear. The downside to blacking out a tank is that many plants won’t survive the process either. In fact, blacking out can be very hard on all but the toughest aquarium plants

UV serilizer

A UV sterilizer takes advantage of the fact UV light kills certain things include algae and some pests and bacteria.

UV sterilizers are usually attached to the return pipe of a canister filter and as the water passes through the sterilizer it kills free-floating algae and bacterial blooms as well as parasites like Ich.

I have good success in my own fish room with the Fluval UV Sterilizer (check the current price of the Fluval UV sterilizer on I simply add the UV sterilizer to any tank that needs it. One sterilizer is all I ever have in my fish room, moving it from tank to tank as required.

Staghorn Algae

Staghorn Algae is another hair-like algae that grows in a branching pattern, often resembling a stag’s horns, as the name suggests!

Staghorn Algae is usually dark grey, light grey, or almost white in color (although it is technically a member of the red algae family). Staghorn Algae is another algae that can quickly take over an aquarium if left unchecked.

Staghorn Algae starts off as small tufts, and as it grows becomes more and more spindly. Staghorn Algae can grow on any decorations in the aquarium and also often grows directly on plant leaves.

The major cause of Staghorn Algae is an excess of iron in the aquarium, usually caused by overdosing on nutrients. Poor circulation and poor light have also been sighted as potential causes in a number of studies.

Whilst Staghorn Algae may look unsightly it doesn’t represent any danger of harm to your fish or plants, although a large outbreak will compete with your plants for light and nutrients, which in the long run may prove detrimental.

To rid a tank of Staghorn Algae I would recommend using the same methods as Black Beard Algae

Green Dust Algae

Much like Brown Diatom Algae, Green Dust Algae can be especially problematic in newly set up aquariums. However, unlike Brown Diatom Algae, there are many reports across the internet of Green Dust Algae appearing after a major change in the aquarium, such as the replacement of a filter or a major trimming of the aquascape.

Green Dust Algae can cover every surface it the aquarium including the glass, decorations, and plant leaves.

I believe Green Dust Algae is caused by a spike in nitrogen, which can be a real problem when a new filter is added to an aquarium or when a large number of plants are removed or heavily trimmed.

As such, my advice for removing Green Dust Algae is just to sit back and do nothing. The tank will soon balance itself out and the Green Dust Algae will be out-competed by the plants.

If you keep Otocinlcus or Bristlenose Plecos in your tank they may well feast on the Green Dust Algae.

Blue-Green Algae (Cyanobacteria)

Whereas the other algae on the list are true algae, Blue-Green Algae is in fact cyanobacteria rather than algae.

Blue-Green Algae grows as a slimy blanket that will cover every surface in your aquarium, killing any plants it covers in the process.

Researchers are currently undecided as to the exact cause of Blue-Green Algae, but many agree that poor water circulation within the aquarium is definitely a contributing factor.

In my experience, Blue-Green algae is especially prevalent in new aquariums which use regular sand as their substrate. This suggests to me silicates in the water may also be a contributing factor.

I am not aware of any fish that will eat Blue-Green Algae. The best way I have found to get rid of it is to manually remove as much from the tank as possible by carrying out a large water change, sucking as much of the Blue-Green Algae up the pipe as possible, then treating the whole aquarium with Maracyn, adding 1 packet for every 10 gallons (38 liters) of water.

Blacking out the aquarium can also kill Blue-Green Algae, but may also kill many of your more delicate plants.

How to Balance Light and Nutrients in an Aquarium?

Balancing light and nutrients involves walking a fine tight rope. Too much light and too few nutrients are a recipe for algae. Go the other way, with too little light, and you have more algae!

In my experience, the best way to balance an aquarium is to start with the light. Every single tank I own has the lights on a timer. For under $10 you can get a simple timer that means your aquarium light is on for the same number of hours each day.

For me, 8-10 hours is the optimum amount of time a light should be on. By setting a timer so the light comes on and goes off at the same time every day, you have half your balancing act in the bag. Next, you just need to balance the fertilizer.

I am going to assume if you are reading this article, you are not mixing your own dry fertilizers. Dry fertilizers are beyond the scope of this article, so let’s ignore them for now.

When I give fish-keeping talks at clubs around the country, the question of algae comes up almost every time. I find the majority of people are using either no fertilizer or an all-in-one fertilizer.

I have used all-in-one fertilizers for many years, simply because I no longer have the time or dedication to mix DIY fertilizers.

So if we assume you have your light on a timer and you are using an all-in-one fertilizer (incidentally I use Easy Green which is made by Aquarium Co-op), you start your balancing by following the manufactures instructions (so 1 pump per 10 gallons of water in the case of Easy Green).

By following the instructions on the fertilizer for 2 to 3 weeks you give yourself a baseline to work from. If after two or three weeks all the plants are growing and there is little to no algae, you probably have things in balance and you just need to keep going.

  • If you find your plants are growing well, but you have excess algae, consider scaling back the amount of fertilizer you dose (but defineatly don’t stop altogether).
  • If you find you have little to no plant growth, but algae growing, considering increasing the amount of fertilizer you dose.

By making small changes and then monitoring for 2 to 3 weeks, you should be able to get a tank dialed in within a couple of months.

In Conclusion

I don’t believe algae is bad for an aquarium, and I certainly don’t fear it showing up in my tanks. If anything, algae can be considered beneficial to an aquarium as it consumes excess nutrients, including nitrates, which build up as a result of fish waste.

By using a combination of algae eaters in every tank along with taking time to balance the light and fertilizer, I can usually keep algae at bay.

If you find your tank has an outbreak of algae, start by trying to decide which algae you have, then take steps to remove as much as you can, then keep it under control using fish, shrimps, snails, chemicals, or a combination.

About the Author

I’ve been keeping, breeding, and showing tropical fish for nearly 30 years. Over that time I’ve done it all! I’ve had great success and I’ve made some really foolish mistakes (like the time I bought an Asain Walking Catfish). Read more…
Richard James

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