The Salty Side: Saltwater Aquariums for Beginners

How To Get Rid Of Green Hair Algae In A Saltwater Tank

Green hair algae, also known as GHA is an extremely common occurrence in the reef keepers world.  Fortunately there are a number a ways to get rid of green hair algae.  This begins with reducing and controlling it, with the eventual aim of eradication.

how to get rid of green hair algae

Why do I have Green Hair Algae in my saltwater tank?

Green hair algae thrives on nutrients. At some point your phosphate and/or nitrate rose to a level that has made your tank the perfect environment for GHA to gain a foothold.

This may have been at the time you started your new tank and phosphate may have been left unchecked for a while. It might have been caused by over-feeding, or it may be that you have no nutrient export in your system. For help with understanding nutrient management (and much more), download our handy ebook.

From personal experience, mine appeared as an indirect result of trying to rid my system of dinoflagellates. I purposely allowed my nutrients to increase, but this had the undesired result of the arrival of GHA.

It is important to understand from the outset that although it appeared so, GHA did not happen overnight. The conditions for it to flourish had to be in place for some time without your realisation.  It stands to reason that you will not get rid of green hair algae overnight either. Eradication will take time and patience.

What fish eat green hair algae?

When it comes to fish they can be as individual as you and I. Many herbivorous fish can and do eat GHA, but whether or not they want to is completely up to them.

Tangs are renowned algae eaters, and can be pretty voracious too. However, as great as they may be you also need to consider if they are the right fish for your tank. Not only do most of them grow fairly quickly and quite large, but you also may end up with that one that will only eat nori.

A Rabbit Face Foxfish is a fantastic algae eater, very well known for eating GHA. I have a Fijian Rabbit Face Foxfish and it does eat green hair algae, BUT if I’m being completely honest I would need a school of them if I wanted them to be my primary control method.

I also have an Algae Blenny but it will only graze GHA that has already been mowed all the way down. It’s preferred meal is the green powdery algae that settles on the glass, and nori.

Fish can be a bit hit and miss!

how to get rid of green hair algae

What invertebrates eat green hair algae in a saltwater tank?

The number one go-to invertebrate for green hair algae is an urchin, such as a Tuxedo Urchin. Urchins are the definition of 24/7 eating machines with one drawback – the GHA has to be low enough for them to pass over. If you have long strands waving around in your tank the urchin will not have any affect at all.

Turbo snails are said to be good, as are Mexican snails, both of which I have. In my experience, if the GHA was too dense or growing from within a rock crevice they simply cannot control it.  In fact, even the urchin, the GHA machine, cannot get into rock crevices.

A sea hare (Dolabella auricularia in particular) is another known voracious Green hair algae eater and may very well have sorted my system out quickly. However, a sea hares primary food is algae, and in the absence of algae they will die. This is why you can often ‘rent’ them from an LFS and return when they have done the job.  My concern with ‘renting’ is that I quarantine everything that goes into my tank (having introduced Marine Velvet unintentionally before).  A sea hare is almost impossible to QT, and I would personally not put it straight into my tank – which counts it out as a method of control for me.

I’ve had to look at additional methods of control and eradication.

How to manually remove GHA from live rock

You may or may not have tried pulling green hair algae from your rock work using your fingers. If you have, you may have found that it is very difficult to pull it away from the rock. When I first tried this the GHA actually started pulling the rock up with it!
The reason for this is the Green Hair Algae is very healthy, very green and actively consuming all your phosphate and nitrate. To get to a point where you can pull GHA out with your fingers (or syphon it out), you need to compromise it’s health.

You need to eliminate phosphate and nitrate from your system.

See I have GHA and no phosphate! below.

Once you have managed to gain control of the phosphate and nitrate in your system, the GHA will begin to become less tenacious. In fact a good indicator that you are headed in the right direction is the ability to remove a pinch full of algae from the base and it comes away easily.

Using a jug/pitcher: Be sure to have a jug/pitcher with fresh water ready, hanging on the side of the tank. After each pinch place the GHA in the jug. This will keep the algae from circulating around your tank, potentially rooting elsewhere. It is also a very direct method of removing the nutrients caught up in the algae. Depending on your tank size, be prepared to spend a loooong time doing this, wrinkly fingers included.

Siphoning the GHA: Using the equipment you would normally use for water changes, remove the large gravel siphon end. If you have a sump, place the end of the hose in a mesh filter sock to catch the algae. Once you have a suction going, place your finger or thumb against the intake, suck in the the algae and use you thumb or finger to break off the GHA strands.
As much as I wanted siphoning to work 100%, I found that it really depends on your rock layout, and where the GHA is growing from. It is easy enough to break algae off an accessible surface, but when the green hair algae is growing from within a crevice the only manual way of removing it it pinching it away.

Scrubbing the algae: This proved to be the best way to get rid of GHA in my tank. You will read that you should remove the rocks to clean them. This is to prevent the spread of the algae, which is true. However, if like me you already have GHA covering everything there is no point in removing the rocks before scrubbing. I did attach a hose and created a siphon to try and minimise the loose algae floating around my display. The nylon scrubbing brush I used was brilliant in getting into all the nooks and crannies.


how to get rid of green hair algae
Siphoning and pinching GHA

I have GHA and no phosphate!

Unfortunately, the above sentence couldn’t be further from the truth. Green hair algae survives on excessive phosphate trapped in the live rock in your system. The reason your test kits are telling you that you have zero ppm is because GHA is highly efficient at absorbing phosphate from the system immediately. This leaves the water you are testing free of detectable phosphate.

If you experience GHA in a very new set up, ensure that you put a phosphate export system in place immediately. This will ensure that you do not allow the phosphate to become bound to the rocks.

With zero phosphate showing up on your test kits, but with healthy GHA growing in your tank, what is your next step?  Phosphate.  It’s all about phosphate.

As I have already laid out what I did, you too will need to put a robust PO4 export system in place.  Don’t decide that this would be a good time to start up a refugium. The truth is, doing so means starting with a handful of cheato or a few fronds of caulerpa.  In such small amounts these macro algaes would never be able to compete with GHA.  If you can get your hands on a sump full of cheato you may be lucky.

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Unfortunately you cannot rely on your test kit for accurate results with GHA in full swing. This does not mean that you should put your test kits to one side though. Your aim now is to monitor your tank as you introduce an efficient phosphate remover such as Rowaphos. Watch the growth of the GHA. If it continues to grow, replace your Rowaphos often. I was replacing every three days at one stage, then weekly. You are looking for a stagnation in growth – and if you’re lucky the green colour of the algae beginning to lose its lustre.

As I’ve explained above, this does not happen overnight. Think in terms of months. When your GHA starts dying back it will release phosphate and you will start picking it up on your test kits.

Killing green hair algae using Fluconazole.

This is how I eventually beat GHA

Fluconazole is the active ingredient in anti-fungal human medication. It is also the active ingredient in a green hair algae treatment. In my experience it completely eradicated my frag tank of GHA, while my main system, not so much the first time (but there is a reason for this which I’ll get to).

My frag tank suffered only a brief spell of GHA. Unlike my main system. The frag tank produces very little nutrients. With the low nitrate and phosphate levels in place and the addition of Fluconazole the green hair algae was fighting a losing battle.

The story is a little different with my main display. Phosphate had inadvertently bound to the live rock due to my war on dinoflagellate.  I realised that I had to extract and export phosphate from the system before Fluconazole worked as I needed it to. While excessive phosphate was bound to the rocks in my tank GHA would continue to grow. 

Using a product called Rowaphos I drove the phosphate down aggressively. I monitored the phosphate very closely. The tests continually showed PO4 as 0.03ppm despite using Rowaphos and changing it out weekly. Visually the GHA in the tank wasn’t growing or dying but eventually after about 5 weeks, the PO4 took a dip and fell from 0.03ppm to 0.02ppm, and continued to fall to zero – now I knew phosphate was actively being exported! In case you are wondering, if you have green hair algae, zero phosphates does not represent the true phosphate value.

With phosphate sitting on zero I noticed the GHA starting to shrink back very slightly. It was still green, but not vibrant. It was time for a far more aggressive approach to manual removal too. As described above, I secured a small nylon bristled scrubbing brush from Amazon to a length of hose with zip ties and scrubbed all of the rock work in the tank. The other end of the hose was fixed into a filter sock in my sump. I also used a fish net to scoop as much GHA out of the water as I could after scrubbing. It was hard work, broken down into 3 days in my 5ft tank. The theory was that my snails, urchin and even fish would be more likely to graze. I also thought fluconazole treatment would be more successful with less GHA to contend with. You will read warnings about not scrubbing GHA in the tank because it will spread, but if you have it everywhere already there is no harm done.

I had used a product called Blue Vet Flux-RX on both systems before. The frag tank had responded amazingly with no adverse affects, but at the time it didn’t work so well on my main display. I decided to give it another go with the GHA scrubbed away, phosphate reading zero, and even nitrate very low at 0.2ppm. This time it eradicated the green hair algae completely. 

I would highly recommend using Blue Vet Flux-RX, and if the need arose I would use it again. However, before using it, you need to do some prep work:

  • Drive your phosphate down to zero and watch for the visual change in the GHA appearance.

  • Drive your nitrates down too. Try to keep them under 1ppm.

  • Scrub your rock work only when you notice no discernible GHA growth, and try to remove as much GHA out of the water as you can.

  • Treat with Blue Life Flux-RX according to the instructions.

Remember if it doesn’t work successfully the first time (as it did not for me), concentrate on keeping those nutrients ultra low to starve out the green hair algae. Then try the treatment again in another month or two.

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To clarify, Fluconazole does get rid of GHA, with the catch that the algae is only relying on daily phosphate introduction (feeding). If phosphate is bound to the rocks you are going to have to work a little harder. 

Using Fluconazole is safe and will have no negative impact on your tank and its inhabitants although you will need to remove some or all of your tanks filtration systems. A 2000mg can treat up to 100 gallons. 

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Using hydrogen peroxide for green hair algae

There is a lot of misunderstanding and misinformation regarding the use of hydrogen peroxide in a reef tank. It is true that if you were to overdose your system it could have very bad results, but your intention is to use it sensibly and in a controlled manner.

I have found that peroxide is a very useful tool when used correctly. I have used it as part of a treatment to gain control of dinoflagellates, and continue to dose to ensure dino do not return.

In addition, it is by far the most effective method of treating GHA directly on the rock out of the tank. Green hair algae can be extremely tenacious, and if like me you are looking for some results, peroxide can be the way to go.

I simply remove one or two of the affected rocks from the system, place them in a plastic container and spray the GHA directly with peroxide 3% concentration.  Don’t be overzealous and dip the rock, or empty a liter of spray over them. Only treat the GHA with one or two squirts and put the rock back in the system as soon as you have done so.

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Peroxide acts as an oxidizer, attacking the Green hair algae. When you place it back into your tank you will notice bubbles rising from the rock. These will subside after about 20 or 30 minutes, and in 4 or 5 days the GHA will turn colour and die off.

It goes without saying that if you have any corals on your rocks, they must be shielded from the spray. Soft corals will be barely affected (I have dipped them in 3% peroxide to rid of green hair algae), but LPS and SPS are far more sensitive.

Using peroxide wisely will also have no negative impact on your tank and it’s inhabitants.


Compared to other algae, it can be relatively easy to get rid of green hair algae in a saltwater tank, but it does take a bucketful of patience. Your number one priority is to get your phosphate and nitrate under control. GHA and nutrients go hand in hand.

If you are lucky enough to land a fish or invert that will control it naturally all the better, but don’t shrug off Fluconazole or 3% peroxide for a bit of extra help.

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