Green Hair Algae Prevention: Handy Hints and Terrific Tips

Charlie Morton

Charlie Morton


Green Hair Algae

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At Aquariadise, we’ve written dozens of articles on algae, so we know how frustrating algae problems can be!

Green hair algae is one type that fish keepers often complain about, so here we’ve dedicated an entire page to find out what it is, how to get rid of it, and to prevent it from coming back.

Key Takeaways

  • Green hair algae is a naturally occurring, yet sometimes problematic algae species that grows in both freshwater and saltwater aquaria.
  • There are several ways to tackle a green hair algae outbreak, including improving water quality, reducing light levels, and manual cleaning.
  • Algae problems are easier to prevent than to cure! The best strategy to avoid blooms is excellent aquarium maintenance and avoiding direct sunlight.

What is Green Hair Algae?

Green hair algae is a type of green algae that grows in long strings that resemble hair. It’s a common, naturally occurring type of algae in both freshwater and saltwater aquariums.

Because it grows quickly and thrives in poor water quality, sudden blooms of green hair algae are both problematic and indicative of an underlying aquarium care issue that needs improving.

Is Green Hair Algae Bad?

While green hair algae isn’t toxic, it can adversely affect your aquarium’s appearance and ecosystem if it gets out of hand. Here’s how:

It Looks Ugly

The most obvious reason that you may wish to remain free from green hair algae growth is that it’s unsightly. Nobody wants an aquarium covered from top to bottom in algal growth, so for cosmetic reasons alone, it’s worth keeping it to a minimum.

It Can Smother Plants and Reduce Light Levels

Green hair algae is not fussy about what it grows on. Aquarium glass, gravel, décor, and live plant leaves are all fair game!

When it grows on aquatic plants, green hair algae prevents them from photosynthesizing, slowing their growth rate or even eventually killing them.

In very serious cases, it may even begin to form hairy mats near the water’s surface, preventing sufficient light from reaching the rest of the tank.

It Can Deprive Your Tank of Oxygen

Like other photosynthetic organisms, green hair algae absorbs carbon dioxide and expels oxygen during the daytime.

At night, however, plants and algae reverse this process. If algae becomes too dominant, it can severely lower oxygen levels at night, depriving your fish and aquatic pets of the oxygen they need to survive.

It Can Adversely Affect Water Chemistry

Algal outbreaks can substantially affect aquarium water chemistry. By suddenly removing essential nutrients from the water column, they can adversely affect plant growth.

Sustained algal blooms can also alter the pH of the water, away from the optimum levels for your fish.

It Can Entangle Fish and Invertebrates

The last reason that green hair algae can cause problems is by entangling small fish and invertebrates in its tangly hair.

How To Get Rid of Green Hair Algae

If green hair algae is growing out of control in your aquarium, you need to act fast to reduce it and prevent serious damage to your fish and plants. Here’s how:

Improve Water Quality

The number one reason that algae become a problem in aquariums is poor water quality. Because algae thrive in water with a high level of dissolved nitrates, phosphates, and other nutrients, reducing these elements is the key to reducing and preventing pest algae.

Improving water quality is a subject you can learn more about throughout the Aquariadise website. Here are some of the key points for maintaining high water quality – please click on the links to learn more about each step!

  • Test your aquarium’s water at least once a month, or any time you notice anything unusual or problematic in your tank. Once you’ve diagnosed which parameters you need to improve, you can work on the source of the problem more effectively.
  • Avoid overfeeding! Overfeeding is one of the greatest causes of poor water quality and fish health issues. Never feed more than your fish can eat within 2 minutes.
  • Get yourself a good aquarium filter and clean it every 2-3 weeks.
  • Vacuum your substrate every 1-2 weeks.
  • Make partial water changes of 15-35% every 1-2 weeks, with treated water of matching temperature.

Remove Algae by Cleaning

If green hair algae is already becoming problematic in your tank, you’ll need to remove it from the various surfaces manually:

Use an algae scraper to remove algae from your aquarium’s sides. Make sure you choose the right type of cleaner according to whether you have a glass or acrylic aquarium.

Rinse your tank décor in warm, chlorinated water. Use a soft brush to remove the worst of the growth. Rinse the items in dechlorinated water before returning them to the tank. Avoid soap as even small amounts are extremely toxic to fish.

Vacuum your gravel to remove algae that’s growing on the substrate.

Gently rub off green hair algae growing on your aquarium plants by hand. If plants are thickly coated, you could also consider an algaecide dip.

Move Your Aquarium Away From Direct Sunlight

There’s an important piece of advice that’s sometimes missed by newcomers to the hobby – that’s to never place your aquarium in direct sunlight.

Since algae are photosynthetic organisms, placing your tank in direct sunlight gives them far more energy to grow and proliferate.

Fish tanks placed in front of a window are extremely prone to algae issues, so if you’ve made this rookie error, place your tank in a darkened corner instead. It will also look more attractive there, glowing under the lighting bulbs.

Reduce Aquarium Lighting Times

In addition to improving water quality and removing algae by hand, you might also want to consider reducing your aquarium lighting hours to further hamper algal growth.

Because green hair algae is photosynthetic, it grows faster when given long lighting hours. Recommendations for the aquarium lighting schedule are normally between 8-12 hours.

Use a timer switch to set your aquarium lights towards the lower end of this schedule, at least until symptoms improve.

How To Prevent Green Hair Algae Issues

Green Hair Algae

Once you’ve dealt with the worst symptoms of your algae bloom, you’ll need to maintain a healthy tank to prevent further outbreaks from occurring.

Maintain Excellent Water Quality

The greatest steps you can take to prevent further algae outbreaks is to maintain a clean tank and keep water quality high. Continue to follow all the steps described above diligently to avoid the problem recurring.

Deploy an Algae Eater To Keep Algae at Bay!

Probably my favorite way to reduce algae is to add fish or invertebrates that love to eat it! Nerite snails and Amano shrimp are two of the best candidates for this job, and don’t multiply in freshwater.

As for freshwater fish, bristlenose plecos are a classic algae eater for tanks of 20 gallons and more, and while some aquarium enthusiasts swear by Siamese algae eaters for green hair algae problems, others have had less success. In saltwater aquariums, consider tangs, blennies, and rabbitfish.

Find out more about the wild world of algae eaters in our dedicated article, here!

Test Your Water Regularly

Your final line of defense against problematic algae outbreaks is to test your water regularly. Get to know your water chemistry so you quickly identify any issues before they become a problem.

In particular, keep an eye on nitrate and phosphate levels and consider more frequent water changes if they get too high.

Additionally, it’s worth testing your tap water to make sure you’re not introducing excessive nutrients when you add more water to your tank.

What Not To Do

It’s worth mentioning here that harsh chemicals are often not particularly effective for treating green hair algae, and they could also severely impact the health of your fish and invertebrates.

Remember that chlorine and soap are both extremely toxic to fish. Even aquarium-safe products often cause imbalances in your tank’s water chemistry, rather than treating the root cause of the issue.

I’d avoid using such chemicals and persevere with the tried and tested simple aquarium management steps that are listed above. Even if it takes some time, these tend to prove to be the most effective methods in the long term.


Green hair algae is a natural component of freshwater and saltwater aquariums, but it can become one of the more troublesome types of algae if it’s allowed to grow excessively.

There are several ways to reduce the amount of green hair algae in your tank, but the most effective strategy is a consistent tank maintenance regime to prevent outbreaks in the first place.

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10 thoughts on “Green Hair Algae Prevention: Handy Hints and Terrific Tips”

  1. I have a 10gal tank that I want to eventually to house neocardina again. I restarted this tank ~1 month ago after having given up on trying to solve the green algae beast on this tank started over 2 years. Dumped everything from old tank, so using all new stuff inside. That means restarting the nitrogen cycle again. Using a mixture of flourite and fluval plant/shrimp stratum with a wide variety of plants (heavily planted with ~11 different varieties including a floating variety to shade part of the tank for the low light varieties). I’m doing a slow restart using only plants to cycle this tank. I did use a bacteria restart ( Stability) and my numbers are still fluctuating where the ammonia is around .25ppm and nitrates at 10-20ppm. Nitrite is 0. GH is 7 and KH is 1. I didn’t want to buy an active CO2 system and opted to try the passive CO2 system from Fluval since it is a small tank. The first tank had no CO2 system and I used Excel for my CO2 needs. I never could get the algae under control. I’ve tried the lower light schedule at 7hrs and then a 4hr on/1.5hr off/ 4hr on/ 15hr off. I have a LED light strip that is 2yrs old and seems just as bright. I just added fert tabs to the soil and was thinking of adding flourish liquid fert (not sure if too soon to add- plants are not necessarily established – last one planted ~1week ago) to support the floaters and to add micronutrients.

    I am NOW seeing the beginnings of the green hair algae again!

    I have a CO2 checker and it never turns green even hours after the CO2 has dissipated from the chambers. I refill the chambers twice daily. Plants look GREAT and pearl (never saw that with my first planted tank). I do 25% water changes with RO water every 10ish days. The light cycle is back to that 4hrs on/off thing I mentioned above.

    Could the cycling of the tank be the cause? Any other suggestions to try before this gets way out of hand?? I don’t plan to add any animals until my test numbers show the cycling is finally stable…

    Thank you for taking the time to read all this! I really would appreciate any suggestions to stop this hair algae. The tank looks so pretty right now and all the plants look very healthy…

    • Hi Susan!
      Well it definitely sounds like you know what you’re doing but your tank just doesn’t care :-). Oh the joys of this hobby.
      It’s very strange that you’re experiencing algae with floating plants; usually, they suck up everything until they overpopulate and the balance goes out of whack again.
      Hm.. quite the headscratcher. I have a few ideas. One, you are dosing too much. You may have overloaded the system with the Stability and root tabs. Two, your lighting is the wrong spectrum/malfunctioning. I also don’t think the staggered photoperiod is helping too much; I think you’re much better off just doing a strict 7-8 hour period. Three, maybe your RO system is malfunctioning/needs a new filter/etc.; make sure to test your parameters from there. These are my main ideas.
      Yes, the cycling of the tank is probably the culprit here, but it could be exacerbated by the factors I mentioned above too. I would try to remove as much of the algae as you can by hand. Maybe bump your water changes up to once every week; it gets tricky here because you want to still have nutrients leftover for your plants, though you should be getting some from the tabs. I would also look into introducing a fast-growing plant or floating plant (like duckweed) that won’t hurt to be removed later on, just to start moving towards a balance.
      Hopefully, your parameters start working with you so that you can start adding snails and a cleanup crew! I hope the algae leaves your tank soon. Let us know how things go.

  2. Hi! I don’t run C02 as it’s a low tech freshwater 10 gallon aquarium. Do I still need to run C02 to get rid of the green hair algae or is there something else I can do?

    • Hi! As described in the article, the alternative would be decreasing your lighting cycle: if you can’t add more Co2, you have to decrease the demand for it. Good luck!

    • Yup, for sure. If there’s no plants to outcompete the algae and absorb all the Co2 and nutrients you’re gonna have a problem.

  3. Hi guys

    awesome information.

    i am struggling with hair algae to the point of depression 🙁

    I have a tank in the wall that measures 1.2m wide by 1m tall and .3m deep. I have white pearl sand, live sand i believe it is, with live rock at either end and a small area in the middle with nothing ( i used to have live rock there and this was the main rock that had hair algae on it so i removed it believing it was leaching phosphates). Now the rocks at either end are covered in hair algae only the side which is facing the large windows which measure 3.6m x 1.5m each and these provide allot of natural daylight the other side of the tank faces the hall way and does not have much exposure to natural light. sitting on top of the tank is a LED light which i purchased from ebay has two settings blue and white light or just blue light.

    I have only a clown fish, 3 chromis, goppi, turbo snail, had a damsil and a royal grammar these passed away.

    i do get the algae film on the glass also this can easily be cleaned with a magnetic cleaner.

    i feed the fish two times a day and i feed them patiently ie make sure all the food is consumed before adding more its frozen shrimp. so i am pretty sure food is not decaying in the tank.

    I have a external water filter with a uv light which i leave on

    I only use RO water. i have had the water tested a few times every time the levels are perfect i have a home kit and measured at home also (everything but phosphate) and again all seems good.

    I dont have any plants or corals other than some coral which has spread by itself long tentacle type white / brown colour this is because again i am patient and luckily children are also wanted to make sure the tank was happy before adding the expensive stuff

    flow seems pretty good as the corals tentacles move around a fair bit not sure how scientific that is.

    If more information is needed i can provide.

    I have not measured CO2 as this is the first i have heard of it to be honest.

    Forgive any mistakes i am a beginner and any thoughts would be greatly appreciated.

    I did try adding a sea hare but it lasted only 2 weeks and did not eat all that much i was contemplating a tail spot blenny but i always prefer rectifying rather than knee jerk solutions if at all possible but he looks like a cool fish may add hoping he can trim this algae down.

    • Hey! Aquariadise centers around freshwater aquariums and I have no experience whatsoever with marine tanks, so I have no idea whether there are factors in marine setups that cause hair algae to appear besides the regular factor of light. So the only thing I can ask is: have you had a close look at your lighting cycle yet? Natural light from windows can be problematic if it’s direct sun. And how long are you leaving the light on for? I’d see how that compares to what other marine aquarists are doing.

      Sorry I can’t be of more help, I hope you’re eventually able to figure it out! Good luck 🙂

  4. Thanks! for such a well written clear and accurate piece of advice. It has tought me a couple of things and confirmed a few things too.

    I too battled the green hair algae and certainly found ‘algae killers’ to be of less than no use.
    In my case I managed to get rid of it without co2. I removed the largest concentrations of it from my tank (sadly it meant my java moss had to go) and then loaded my external canister filter with coal ( generally used for removing unwanted chemicals) and that fixed it. ( I also did less than a quarter water change). No algae issues at all in the past 3 years 🙂


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