Is Green Algae Good in a Freshwater Aquarium? (Complete Answer)

Algae is probably one of the most hated things by aquarists, battling for supremacy with aquarium snails. But despite the fact that it’s not really beautiful to look at, not all algae is bad for you aquarium. Actually, most isn’t!

Green algae is the most common type of algae that appears in aquariums and the most common cause for green water in your tank.

It can stick to the glass of the aquarium, your other plants, the substrate and/or hardscaping elements or decorations.

But green algae is not bad for an aquarium, on the contrary. If green algae appears in your tank, it means that the water quality is good, but you might have too much light (or too strong of a light) or maybe you are not changing water often enough.

green algae on glass of my tank
Green algae growing on my jarrarium’s glass and plants

It won’t directly harm your fish unless it grows into a thick, unpassable mass (which is highly improbable).

Some aquarists claim that it can consume the nutrients that your aquarium plants need – but then again, it should be in very large quantities in order to be a problem.

What does green algae mean in a fish tank?

Your aquarium might suddenly be overtake by green algae. Such an algae bloom can happen over night and it can be cause by excessive or improper lighting.

If you keep your tank near a window or on a windowsill and the sun is stronger one day, it can result in an instant green algae bloom.

The same can happen if you forget the led lights turned on or you use too strong of a led light setup for the size of your tank.

Green algae can also develop naturally (albeit at a slower rate) in properly lit and maintained aquariums, while at the same time they can appear and bloom if there are too many nutrients in the tank.

But green algae doesn’t necessarily mean that there’s something “bad” with your aquarium. It’s just something that naturally grows underwater, like all types of algae.

However, it’s most likely caused by improper lighting (either led or natural light) and it’s usually easy to see if that’s indeed the cause, because there’s more algae grown where the light is stronger – such as on the glass that’s facing the sun or in the area where the light shines the brightest.

This type of algae is also very common in jarrariums. I absolutely love creating jarrariums – which are usually no maintenance – and in almost all cases, I’ve seen more or less green algae growing inside or on the sides of the glass.

green algae in small jarrarium
Even my tiny moss ball jarrarium has green algae overgrowth

I personally enjoy it, as I want my water ecospheres and tanks to have a “natural” look and not that picture-perfect design that many aquascapists aim for.

But this is just a matter of personal preference and it’s OK not to want any type of algae in your tank.

Is green algae bad for my aquarium?

No, green algae is not bad for an aquarium, on the contrary. It can provide your living animals inside an extra dietary option. Fish might munch on it, but shrimp and snails will consider it delicacy.

However, it can look bad if left unattended. If it grows on your tank’s glass, it can also make seeing inside the aquarium more difficult.

As I said, some people also claim that green algae can eat up the nutrients your other plants need, but in order for that to make a difference, you need a huge overgrowth of green algae and almost no nutrients in the water – which is a highly unlikely scenario.

Bottom line, while green algae is not necessarily good in an aquarium, it is not bad either. Most people choose to remove it as soon as it appears in order to keep their water crystal clear and the overall look of their aquarium fresher and nicer.

How to get rid of green algae in a freshwater aquarium

There are multiple ways to get rid of a green algae bloom, but the best option is to resolve the cause, otherwise you will have to deal with it again. So in this case, prevention is the best cure.

However, if you already have a green algae bloom that you have to deal with – or just some overgrowth that you don’t like, you have multiple options on hand that will help you get rid of it.

Here’s what you need to do:

1. Do a partial water change

Bring in fresh water in order to keep the algae bloom under control! Do a partial water change (around 30% of your tank’s water), then do another water change after 4 days.

This will keep the algae under control and remove much of the excess algae that is free floating in the water.

green algae on plant in aquarium

2. Clean the aquarium glass and decorations

If the green algae is starting to stick onto your aquarium’s glass and/or decorations, it’s time to clean that up manually.

Use a regular (but never used before) kitchen sponge to thoroughly clean the glass of your aquarium. You can also use a brand new toothbrush to reach the trickier places and corners of your tank.

If possible, remove the decorations from the tank and give them a proper cleaning, then let them dry completely before putting them back into the tank. Before that, rinse them in cold water again.

3. Properly clean or replace the filter

Replacing the filter shouldn’t be done too often, but if it’s been a long time since you last replaced it, now it might be a good time to do so.

Otherwise, properly clean your filter – especially the sponge or filtering media if it’s an external one – as that’s where most of the algae will be in.

Clean the filter in water from your aquarium (or at least dechlorinated water), otherwise you will destroy the beneficial bacteria living there, resulting in an upset water balance which might result in an even bigger algae bloom.

4. Reduce or change light

Since improper lighting is most likely the main cause why you see so much green algae in your tank, you have to deal with that.

If your aquarium sits in direct sunlight, find a new position for it. I know, tricky. If impossible, find a way to offer shade during the time when there’s direct sunlight hitting the aquarium.

If you use artificial light, you can simply turn it off and keep it like that for a day or two. Your plants won’t suffer a lot, but the algae won’t multiply anymore and in combination with the other measures, it will be kept under control.

Alternately, reduce the light hours to 2-4 per day for a few days, until you get rid of the green algae.

5. Buy an UV sterilizer

These sterilizers are great in controlling algae overgrowth and dealing with this problem. They will need some time to clean the water in your aquarium, but they will get the job done eventually (in around 4-7 days).

If you constantly have problems with green algae in your tank, an UV sterilizer might be your easy way out. My recommended one is the Codia UV sterilizer (affiliate link).

6. Buy livestock that eats algae

This is my favorite way of dealing with algae! Invest in some Red Cherry Shrimp, Amano shrimp (or basically any type of shrimp) and they’ll love to feast on your algae.

Adding snails to your tank will also help a lot with the problem, but depending on what snails you bring in, you might end up with a snail infestation to replace your algae bloom.

But usually Nerite snails are great for aquariums (albeit a bit slow), as well as one large Apple Snail, as it won’t multiply if it’s just one.

While none of these measures will solve your problem overnight, they will help and eventually you will get your crystal-clear water back.

Remember that you will always have some algae in your aquarium – it’s just the way these ecosystems work, but keeping it under control is easier if you follow the methods recommended above.


Hopefully you had all your questions related to green algae in aquariums answered. If you still have doubts or any comments to make, don’t hesitate to write a few lines below and I will answer as soon as possible.

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