HLLE – Head and Lateral Line Erosion Disease Treatment

What is HLLE?

HLLE is a disease that afflicts many of the ornamental marine fish in our hobby.  The acronym stands for Head and Lateral Line Erosion.  Fish suffering from HLLE will develop pitted holes that usually start around the eye area and continue, forming a line towards the tail.


Surgeonfish and angelfish are the most common families of saltwater fish to suffer from HLLE, but other families of marine fish have been known to develop the disease as well.  HLLE is rarely fatal, but if left untreated it will cause horrific and permanent scars on the animal.  The main threat to the life of the fish is from secondary infections that can result from the open wounds created by HLLE.


Head and Lateral Line Erosion disease does not impact many fish outside of the saltwater aquarium hobby.  Lack of commercial interest has resulted in almost no funding for proper scientific study of the disease.  This has caused HLLE research to be mainly conducted by hobbyists.  Rampant speculation, anecdotal or outright conflicting evidence constantly swirl around the affliction.

What Causes HLLE?

The true cause of Head and Lateral Line Erosion disease is widely disputed.  There are many opinions on the matter and few studies offer any concrete evidence.  I will do my best to clear up any confusion about what you are likely to hear while researching the disease.


I have personally dealt with HLLE with my fish and have had some success treating it over the years.  My opinions on the topic were formed from comparing countless sources as well and my own experiences.

HLLE Theory #1 – Poor Water Quality

Maintaining good water quality seems like common sense, but is often overlooked.  Overfeeding, overstocking and undersized filtration will all cause poor water quality.  This can result in your fish developing bacterial infections and other ailments.


Compare your aquarium water to the air we breathe.  Think of a life where you’re surrounded by crisp mountain air and then imagine moving to a polluted city, with smog so dense you can taste it.  I’m sure you will agree that living in the smog will damage your lungs and increase your odds of getting sick.


Polluted water may or may not be the cause of HLLE, but healthy water parameters are vital for the recovery of any fish suffering from any disease or infection. Remember, Head and Lateral Line Erosion leaves open wounds and hinders the immune system of the fish.  Combining HLLE and poor water quality can be a fatal one-two punch for your fish.

HLLE Theory #2 – Poor Diet

Numerous hobbyists, including myself, believe that nutritional deficiencies are a leading cause of Head and Lateral Line Erosion. A common link among the fish most susceptible to HLLE is their diet in the wild.  Surgeonfish are primarily herbivores and spend most of their lives grazing on marine algae. However, many fish in captivity are forced to change their natural eating habits because they are housed in community tanks.


If your fish tank was dedicated to the surgeonfish family you would exclusively feed them algae to best replicate their lives in the wild.  However, this is rarely the case because we tend to keep herbivores along with carnivores in the same aquarium and feed a food that both will accept.

Blue hippo tang with permanent HLLE scars

Pellets & Flakes – Microwaved Burrito of the Sea

New hobbyists will often use pellets or flakes as the primary source of food for their fish. This is usually for the sake of convenience or because they may not know any better.  Unfortunately, many brands of pellets and almost all brands of flakes can quickly pollute your water or cause health issues with your fish.


Imagine living your entire life and only eating microwaved burritos and vending machine food from the local truck stop.  You will survive, but how much will your health suffer as time goes on?


Scurvy was a disease that ravaged sailors in the 1700s.  Scurvy makes its victims tired and weak, causes swollen gums and teeth would even begin to fall out! This disease was the result of a poor diet with little or no vitamin C.  Isn’t it reasonable that the health of your fish will also suffer from a poorly structured diet?

HLLE Theory #3 – Activated Carbon

The main evidence about activated carbon being a cause of HLLE stems from two studies performed almost a decade ago, between 2010 and 2011.


The Journal of Aquatic Animal Health published “Effects of Full-Stream Carbon Filtration on the Development of Head and Lateral Line Erosion Syndrome (HLLES) in Ocean Surgeon” in Volume 23,Issue 3.


This study was conducted with by the Walt Disney World Resort using extruded coconut shell activated carbon, more commonly known as pelletized carbon.


They found that all the surgeonfish exposed to the carbon displayed HLLE symptoms within 15 days and the fish had a full recovery within 49 days after removing the carbon from the test systems.


A second study was published a few months later in Volume 73, Issue 4 of the North American Journal of Aquaculture.  Titled “The Role of Activated Lignite Carbon in the Development of Head and Lateral Line Erosion in the Ocean Surgeon” by Jay Hemdal and R. Andrew Odum.  This study expanded on the findings of the previous one by using thirty-five ocean surgeons and testing two types of carbon.


The fish that were exposed to the activated lignite carbon or the pelleted carbon all showed the pitted wounds of HLLE within 90 days of their study.  The fish without any carbon exposure in the control tank did not develop any lesions, just like the Walt Disney World study.

Carbon Conclusion

You can click here to check out an example of premium carbon

Many hobbyists have used these studies to justify removing carbon from their aquarium filtration systems.  However, I believe this is not as simple as carbon being the root cause.  The prevailing theory is that the tumbling of the carbon releases a fine dust into the water that will irritate or damage the scales and cause the HLLE disease to manifest.


Think of it as living in a minor sandstorm for most of your life. It’s not surprising that the constant micro-abrasions to the skin could cause an infection of some sort.  Activated lignite and extruded pellet carbon are both well known for being soft and generally of low quality.  There are also many reports of aquarium hobbyists running higher grade activated carbon and never seeing a single case of HLLE in their systems.


I would wager that the quality of the carbon and filter flow-rates are substantial factors in generating the harmful carbon dust particles that may be cause HLLE.

HLLE Theory #4 – Stray Voltage

Stray Voltage in an aquarium is caused by damaged equipment that leaks AC voltage and current into your tank water.  Many in the reefing community believe stray voltage is a cause of HLLE and many other issues in aquariums.  Stray AC Voltage can be detected by connecting a multimeter to an AC receptacle’s ground and your tank water

Click the image for a quality meter, but a free one from Harbor Freight works too.

Extreme cases of stray voltage can result in receiving a nasty shock when sticking your hand into the aquarium. It is more common than you think! I wrote about the old Hydor powerheads and their legendary ability to electrocute reefers in my Ultimate Reef Aquarium Setup Guide.


Stray voltage is a very real, yet widely misunderstood phenomenon. It has also become an infamous scapegoat and boogeyman in our hobby.  I could dedicate an entire article to stray voltage, so I will keep this brief.  Leave a comment if you would like to learn more about the subject.


Magnetic driven devices, such as our pumps and powerheads can cause a low AC voltage reading in aquariums.  This is completely normal and caused by induced current from the magnetic field that’s generated to spin the pumps.  These stray AC voltage readings are often demonized and incorrectly blamed for many unrelated issues.  Readings between 10Volts and 30Volts are common in most tanks running AC powered or magnetic driven equipment.


Higher readings near your household voltage are possible and will mean that you have a damaged piece of equipment in dire need of replacement.  GFCI receptacles will normally trip in this situation and are highly recommend for the safety of yourself and your family.

Aquarium Grounding Probes

Grounding probes are a hugely debated topic.  This is a simple cord with one end that plugs into the ground pin of your electrical outlet with the other end submerged in your fish tank.  Aquarium grounding probes create a safe path for AC voltage and current to travel and protect you from getting zapped.


Some reefers will not setup a tank without one, while others believe they are causing more harm than they prevent by randomly tripping GFCI circuits.  You purchase a quality, titanium ground probe for less than $20 here. 

This is a standard aquarium ground probe (click)

Stray Voltage Conclusion

As I said, stray voltage can be a real danger when it is caused by damaged equipment.  It will also come up in almost every debate or forum thread as a possible cause for any complex problem.


HLLE? Stray voltage!  Coral is suffering? Stray voltage!  My fish gave me an angry glance…? You guess it, Stray voltage!  You can see where I am going with this.  I personally do not put much stock in stray voltage as a cause of HLLE.

HLLE Treatment & Prevention

The true cause of HLLE may not be scientifically proven, but we still have some successful methods to treat the symptoms.

  • Feed fish a varied diet that includes seaweed and a vitamin supplement, like Selcon.
  • Keep water parameters in a safe and healthy range
  • Only use high-quality carbon and reduce flow rates to avoid releasing abrasive particles into the water
  • Check for damaged equipment that may produce stray voltage. This is more for your safety than treating HLLE, but it can’t hurt, right?

It’s the responsibility of everyone in our hobby to learn about the dietary requirements for every animal we plan to keep.  Yellow tangs, Blue tangs and every other variety of surgeonfish require algae in their diet.  I use a simple feeding clip, like this one sold on Amazon.  I offer my fish seaweed twice a day, Omega One Seaweed is also available on Amazon or from your LFS.  You can purchase Nori in bulk at your local Asian market or organic food store.  It is VERY IMPORTANT that you only use raw and unseasoned Nori!  Nori that is salted or flavored will harm your tank, so when in doubt buy seaweed sold as fish food, like the Omega One products.

Daily seaweed is important for the health of your surgeonfish, but vitamin enriched seaweed is even better!  I highly recommend soaking food in Selcon before offering it to your fish.  You can click here to purchase a bottle of Selcon for about $15.  You should only use a few drops at a time, so the bottle will last awhile.  Again, I highly recommended this supplement for all your fish.  I have personally used it to heal a yellow tang with HLLE, so it’s the real deal.

Variety packs are great for finding the kind they like best

Carbon gets a lot of the blame for HLLE and most reefers will avoid it completely.  I tend to only use carbon for brief periods as needed to treat a specific issue.  Carbon is great for removing discoloration, medications and other chemicals from your aquarium water.  Many reefers run Granulate Activate Carbon (GAC) 24/7 to improve water clarity, but some prominent members of the reefing community believe this is a mistake.   Marc Levenson, of melevsreef.com, has expressed concerns about carbon becoming exhausted and ineffective in as little as a few days.  Marc advises only using carbon for a few days a month or as needed.

Managing the Effects of HLLE

Everything, but the eye has healed in 10 months

There is Still Hope!

Head and Lateral Line Erosion disease should not be an issue if you follow my suggestions.  Remember, the damage from HLLE is 100% reversible if you catch it early enough.  Fish can also recover from severe cases of HLLE by taking these steps. Just like a person would have a chest scar after heart surgery, your fish may have permanent scars after recovering from the disease.  This is to be expected and the fish can still live a long and otherwise healthy life.

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Picture of Phil Beauregard

Phil Beauregard

A man with a beard, that you can trust! Phil Beauregard is a business consultant and entrepreneur that has been addicted to fish keeping since childhood. He grew up with stories of his grandfather’s exploits during the early days of reef aquariums and African Cichlid breeding. Phil brings a flair for high tech DIY projects and his love of teaching others to the reefing community.

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