Why Are My Goldfish Fins Turning Black?

Goldfish is one of the top aquarium fishes and are most aquarium owner’s top choice. This preference is because goldfish is easy to care for and does not have strict environmental demands.  The colors can, however, change with varying conditions of the tank.

Goldfish Fins Turning Black

Why Are My Goldfish Fins Turning Black? The most common reason for a goldfish fins to turn black is fin rot which is usually caused by the amount of ammonia present in the tank. It can also be as a result of disease, water conditions or natural color change. 

If your whole goldfish is turning black take a look at this article that I wrote about why goldfish turn black.

Causes Of Goldfish Fins Turning Black

The most common reasons for your goldfish fins turning black include

1 . Fin Rot

If your goldfish has fin rot this will cause the fins to look black in colour.  The most common cause for fin rot is poor water conditions.  The disease is also contagious so if you notice a goldfish with the disease it is important to seperate them from the other fish as soon as possible,.

To treat fin rot you will need to do the following

  • Make sure the tank is clean
  • Use an aquarium water test kit (Available on amazon) to make sure the water conditions are ok
  • Treat the water with Mardel Maracyn (Available on amazon)

2. High Ammonia In Tank

Excessive ammonia in goldfish environment is another primary reason why their fins can start turning black. High ammonia content can cause chemical burns all over their body, particularly in specific regions like their fins. These burns lead to significant color change to the collection and fins of goldfish.

Ammonia hikes in tanks are dominant as a result of rotting food and the accumulation of fish waste in the tank. If the ammonia level is kept high for a long time, it won’t give the goldfish enough time to heal up.

You can prevent excessive ammonia hike in your tank by carrying out the natural cleaning process in the tank. This regular cleaning can help you get rid of the accumulated waste in the tank. Likewise, it would be best if you considered changing your aquarium regularly to prevent ammonia build up in the tank.

Similarly, the feeding pattern of your goldfish can affect the level of ammonia build up in the tank. If food is leftover in the tank, it can start rotting, consequently leading to ammonia buildup in the tank. It is best to feed goldfish with a moderate amount of food that the goldfish can finish in 2-3 minutes and get rid of any leftover as soon as possible.

3. Poor Water Conditions

Your aquarium might be suffering with poor water conditions, the best way to rule this in or out is to Use an aquarium water test kit (Available on amazon)

A lot of things must be kept in place to make the environment favorable for your goldfish. You should ensure proper oxygen circulation and water movement in goldfish tanks to ensure that they stay healthy. They also need partial water change about once a week to ensure the cleanliness of their tank.

The consequence of leaving your goldfish tank dirty can be as extreme as the death of the fish. You should also avoid overcrowding in the goldfish tank, and you shouldn’t keep them with aggressive and temperamental tank mates. Their gentle nature makes them quite susceptible to being bullied. Similarly, other essential factors like pH, temperature, alkalinity, and hardness should be kept in check.

Addition of plants to goldfish tank is a valuable addition. The presence of plants in goldfish tanks can make the tank simulate the natural environment of the fish, and also give the goldfish tank a befitting look. It can also provide a hiding and resting place for the fish. Likewise, it can help in the natural cleanup of the tank and improve oxygen circulation

4. Natural Color Change

Some times there is no issue at all and your goldfish will change color for no reason at all.

5. Other Illness

The case of goldfish fin turning black because of disease is scarce, but that does not mean it can’t happen. Parasites cause most of these illnesses, and these parasites find their way into the fish aquarium by different means.

One of the dominant ways parasites find their way into a goldfish tank is by the aid of water snails. These parasites then burrow themselves into the skin of unsuspecting and vulnerable and unsuspecting goldfish. Black fins are one of the ways the parasites physically express themselves in goldfish.

The eggs of these parasites often survive in goldfish by protecting themselves with a hard, dark cyst. The parasites, however, find it hard to find a place in clean tanks and healthy fish. Adult goldfish are also less susceptible to the parasite invasion. They can, however, display irritation by continually flicking their bodies.

Parasites can cause goldfish to change from its original shimmering color to an overall blackish color. Numerous factors can make goldfish susceptible to the invasion of these parasites. These factors include stress, unfavorable water parameters, old age, or dirty tanks.

Getting rid of this parasite is quite easy, and swift action must be taken before the entire tank community becomes susceptible. Removing snails from the aquariums can break the life cycle of the parasite, thereby preventing its spread. Likewise, keeping the tank clean and ensuring your goldfish stay healthy is another effective way to protect your tank.


Goldfish are colorful and active aquarium fishes. You can quickly figure out there is a problem if the color of the goldfish starts turning black. The fins are one of the parts that can significantly tell if something is wrong once it turns black. The primary reasons for this black color are because of hike in ammonia level of the tank, disease, or natural color change.

Nevertheless, here is the goodness. The black color of the fin is not life-threatening if swift action is taking. Simple steps like keeping your tank clean, regular water change, good feeding habit, tank decongestion, and regulation of ammonia level can save the situation in check.

The fins of goldfish can be a profound source of concern for aquarium owners. Black fins in goldfish can be as a result of several reasons.

Ammonia burns might not be evident on the skin of the fish at that instance, but black patches often show up on the surface once the ammonia level drops. These black patches often appear on the fin or even elsewhere on the skin. Likewise, the presence of parasites in the water and other unfavourable water conditions can cause the fin of your goldfish to turn black.