Why Is My Puffer Fish Turning Black? {Causes, Symptoms, Treatments & Prevention}

Are you concerned about your Puffer Fish turning black, do you know why is my puffer fish turning black?

Do you also see an increase in black spots? Is your Puffer Fish sick or camouflaging itself?

In this article, we’ll focus on why your Puffer Fish is turning black. We’ll review some possible illness indicators and discuss camouflage as well.

Why Is My Puffer Fish Turning Black?

Poor water chemistry, stress from poor acclimation, diseases, infections and inadequate tank sizes may create a darkening hue on your Puffer Fish. You may actually be noticing a camouflage effect by using a dark substrate or dark decorations and backgrounds.

Do Puffer Fish Change Color?

The environment around a puffer fish influences it in terms of the color it wishes to display. Obviously a puffer fish is not the same as a chameleon, but the camouflage effect has been noticed in certain species.

It may be a subtle lightening or darkening shade to match the background, substrate or decorations in and around your tank.

Experiment with a lighter substrate such as sand, and consider placing the location of the tank in front of a lighter colored background.

Why Do Puffer Fish Turn Black?

The beauty and graceful swimming patterns couple by the various colors on a puffer fish makes it so appealing to members of the fish keeping community.

The dark shade or blackening appearance can be alarming or concerning at the very least. It’s important to spot this right away and determine what could be causing it.

Look for symptoms associated with a puffer fish turning black such as:

  • scattered black spots all over the body and gills
  • struggling to breathe
  • swimming erratically or up and down nonstop
  • excessive hiding
  • leaning or swim bladder buoyancy issues
  • lack of appetite
  • lethargic
  • fins clamped
  • excessive mucus coating
  • rubbing against objects and glass walls
  • fin rot
  • cloudy eyes

The water levels must be tested at this point where you notice one or more of these symptoms alongside the blackened color or shade of your puffer fish.

What Made My Puffer Fish Become Black?

Are you seeing spots peppered all over your puffer fish? Are these changes happening to the overall hue of your puffer fish? Are they temporary or not reverting back?

If the situation is temporary, you may equate it to a camouflage effect, especially if you have a dark substrate or background. Black spots indicate infections or illnesses that require medical treatment.

Color changes that happen slowly and do not revert back could be explained by the following factors:

  • stress
  • old age
  • poor water conditions
  • acclimation into your tank was rushed
  • tank is too small

Consider tank size first at this point:

  • 20-30 gallons = small sized puffer fish
  • 100+ gallons = large puffer fish

Then look into water parameters:

  • Water temperature: 75 to 79 degrees Fahrenheit
  • pH levels: 7.0 to 7.6
  • Water hardness: 10 to 25 KH

Medical treatment or correcting the water chemistry is at the forefront for helping restore the lighter color of your puffer fish.

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Why Did My Puffer Fish Suddenly Become Darker?

If the color change you are noticing happened overnight, then we must consider a sudden change to your water chemistry.

Water Chemistry Tests

If your tests are turning out correct, you might need a second opinion at your local fish shop with a water sample. An API Master Test Kit is recommended over test strips.

Poor Acclimation

Another factor could be that you have brought in a new puffer fish and it turned black right away due to improper acclimation.

You must employ the “drip acclimation” method with gradual and patient care. Research the drip acclimation process if you are not aware of using this practice of introducing new fish into your tank.

Instant stress from this may have resulted in your puffer fish turning black so quickly.

Did My Puffer Fish Turn Black Because It’s Sick?

Look for other signs including a loss of appetite or abnormal swimming patterns. A bacterial infection or something fungal that entered the tank could have occurred.

Parasites may also be considered as a possible reason why you notice black spots peppered across the body of a puffer fish.

If the color change is accompanied by any other undesired symptoms, it could be treated with medication. Here a a few examples of bacterial, fungal or parasitic infections:

  • Spironucleus spp
  • ichthyophthirius multifiliis
  • Aeromonas hydrophila
  • Fusarium solani
  • F. moniliform
  • F. oxysporum

Remember when using medication, you should remove the carbon from your filter or else the medicine will get sucked in and limit its ability to treat your sick puffer fish.

How I Treat A Puffer Fish That Has Turned Black?

Consider a larger tank if your particular species of puffer fish requires it.

Although you may find information to indicate that a 10 gallon tank could house one dwarf puffer fish, we recommend at least 20 gallons. Larger types of puffer fish need 100 gallons or more.

Perform the following steps to treat your puffer fish that is turning black:

  • Test the water levels.
  • Look for symptoms of illness such as cloudy eyes or loss of appetite.
  • Add an air pump for extra water circulation.
  • Clean the substrate.
  • Perform larger than normal water changes at 50% or more.
  • Add aquarium salt to the tank at 1 tablespoon per 5 gallons.
  • Decide to treat the tank with Melafix or other remedies after discussing the options with a vet or a knowledgeable expert of puffer fish at a reputable fish shop.

How Do I Prevent My Puffer Fish From Turning Black Again?

If you have taken the successful steps to bring back the color of your puffer fish and wish for this to never happen again, you can try the following practices:

  • Perform weekly water changes.
  • Test the water chemistry more often with an API Master Test Kit.
  • Use a lighter colored substrate.
  • Keep the decorations and background light in color.
  • Get a larger tank.
  • Do not let leftover food remain in the tank.
  • Feed more nutritious meals and add liquid vitamin solutions such as Selcon.
  • Dip food in liquid garlic to boost immune system.
  • Drip acclimate any new fish.


Determine if your puffer fish is using camouflage to blend in with darker surroundings. Add more lighting throughout the day.

If you notice abnormal behaviors coupled with the darkening complexion of your puffer fish, then it’s time to act on it with medication or a tank clean up. We hope this issue corrects itself with your care and patient management.


Thanks for stopping at HelpUsFish.com and see you again soon for another article on puffer fish or a multitude of marine and aquatic life we enjoy as much as you do. 

Brian Arial

Brian Arial has kept fish for leisure and worked with fish stores for most of his life. He enjoys writing and caring for aquariums and ponds.