HLLE and the Activated Carbon Connection

HLLE in an ocean surgeonfish (Acanthurus bahianus) caused by the use of activated carbon.

HLLE in an ocean surgeonfish (Acanthurus bahianus) caused by the use of activated carbon.

Many different factors have been considered as possible causes of the disease known as Head and Lateral Line Erosion (HLLE)—a condition that typically causes disfiguring tissue erosion on the head and along the sensory lateral line of certain marine fishes. Poor water quality, nutritional deficiencies, protozoa of the genus Hexamita, stray voltage, and activated carbon use are just some of the potential causes that have been floated over the years.

However, as Jay Hemdal explains in the following excerpt from his new eBook, The Salt Smart Guide to Preventing, Diagnosing, and Treating Diseases of Marine Fishes, there is now some solid scientific backing to the notion that activated carbon can cause this condition.

From Chapter 3: Husbandry, Environment, and Your Fishes’ Health

“A relationship between the use of activated carbon in aquariums and the development of HLLE in surgeonfish has been positively shown in two scientific studies. Other than that, no formal studies have been undertaken that identify other causes. However, a multitude of unproven causes have been presented by various people. Commonly, stray electrical currents and vitamin deficiencies are cited as causes, but one of the studies mentioned above ruled these out as common causes.

Based on those preliminary observations, the Toledo Zoo performed a study that demonstrated that, indeed, lignite carbon causes HLLE in surgeonfish. Minor HLLE lesions were noted on two study fish 20 days after the lignite carbon was added to the sump of their system. The lesions began to develop on the additional fish in that system and grew in size until after four months, all of the fish in that system showed severe lesions (eventually involving over one-third of their body surface). The control fish did not develop any lesions.

The carbon study hypothesis

The basic hypothesis of this study was that activated carbon causes HLLE in fishes. Originally, it was thought that carbon dust (known as fines) was the causative agent. This was based on observations at the Toledo Zoo where carbon was removed from an aquarium and the water was changed, yet HLLE symptoms could still be produced by adding susceptible fish to the aquarium, indicating there was some unknown residual action by the carbon.

Carbon fines were frequently discovered in the filter sumps and substrate of these tanks. Changing all of the aquarium’s water, decorations, and substrate would then render the aquarium safe for housing susceptible fishes (assuming no new carbon use).

Two public aquariums have reported acute outbreaks of HLLE in systems where carbon had been accidentally ground up and ejected into aquariums by mechanical filtration systems. It has also been reported that aquariums that use protein skimmers (foam fractionators) do not seem to develop HLLE as frequently, even when carbon is routinely used. Since protein skimmers remove particulate organic carbon from water (including carbon fines), it was thought that this might be the reason these systems do not cause HLLE as readily.

In addition, the hard-pelleted carbon used in this study did not cause severe HLLE, while the soft, dusty carbon did. However, no carbon fines were seen during histological examinations of the lesions of the study fish. This means either that the dust causing the effect is fleeting, the fines were too small for the histologist to see, or there is some other factor associated with carbon use that causes HLLE in susceptible fishes.”

The Salt Smart Guide to Preventing, Diagnosing, and Treating Diseases of Marine FishesFor more information on HLLE, including symptoms (did you know that yellow tangs tend to be atypical in this regard?), vulnerable species, and recommendations for activated carbon use, get your copy of The Salt Smart Guide to Preventing, Diagnosing, and Treating Diseases of Marine Fishes.

Photo credit: Jay Hemdal


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. Matt Filippi says

    Well that just stinks. So pellet carbon may be ok? What about Cemipure?

    • Hi Matt! Based on the study’s findings, it does appear that hard-pelleted carbon might be a safer alternative. I’m not sure what type is used in Chemipure, so I can’t comment with any authority on that particular product. Also, I would emphasize that not all fish are going to automatically develop HLLE if carbon is used in their system. I think the takeaway is that carbon use might be contraindicated for certain susceptible species.

      For example, I have had two separate personal experiences in which the onset of HLLE symptoms in yellow tangs was correlated with the introduction of carbon. Was it causative? I can’t say for sure. However, in both instances, after moving the fish to a different system without carbon, the erosion quickly abated and began to heal. Again, this is purely anecdotal, and there’s always the possibility that some other factor was in play, but I found the correlation quite curious.

  2. Matt Bowers (Muttley000) says

    This topic has always seemed to bring out the passion in those who don’t believe in the possible negative effects of running carbon. If I remeber correctly people who disagreed with Jay on this topic were the reason we don’t have his thoughts available on the largest reef forum out there any more, which is a true shame.

    • Jeff Kurtz says

      So true, Matt. Our philosophy is that it’s always best to give people access to information, even if it might generate a bit of controversy. Those who disagree are then welcome and encouraged to share their viewpoints (provided they do so respectfully, of course) so that readers can see all different sides of an issue.

      • SIR,
        I am from INDIA and want to buy “The Salt Smart Guide to Preventing, Diagnosing, and Treating Diseases of Marine Fishes.”book. I can’t afford buying from amazon.com/UK.

        Please please please SIR help me.

    • Chris Aldrich says

      It’s interesting you’ve brought this up, Matt, as I’ve been “fighting the good fight” in various places online since we published this post. It really is a polarizing topic that gets folks riled up. Below is the response I’ve been giving to said hobbyists:

      “It’s important to note based on two formal studies that have been completed, both revealed a connection between activated carbon and HLLE. I visited Jay while he was conducting his study and it was solid work (it was also peer reviewed, by the way).

      More work needs to be done on the topic to understand the complexities, but the results of both suggested there is, in fact, a relationship. Any other reports on either side of the debate are purely anecdotal. There are simply too many variables at play outside of a controlled environment.

      Should this stop you from running carbon if you keep tangs (or other susceptible species)? No, but it’s something to be aware of. Also, utilizing high-quality carbon, thorough rinsing, and protein skimming appears to mitigate the risk.”

  3. I am going to do a test of this. I have not run any carbon on my tank in probably 5 years and as of now, I don’t have any tangs. For many years I always had a hippo tang in my tank but they invariably developed HLLE and looked like they got run over by a school bus, twice. The next time I am at an LFS I will buy a small hippo tang to see if it develops HLLE. I am on the fence about this carbon thing but will reserve my opinion until after this test that will last about 5 or 10 years. I will let you know what happens.

    • Lignite carbon is the culprit. It is a very soft dusty carbon nearly impossible to wash clean with the slightest movement causing more dust. This dust causes HLLE as it attaches to the fish and somehow eats at the HLL. Do not use this carbon. I have been keeping marine fish 20 years. 900 gallon marine tank and 125 reef. 19 yellow tangs for many years no erosion.

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