Why Are My Goldfish Fins Turning Black? | Aquascape Addiction

Why Are My Goldfish Fins Turning Black?

We cover the main 3 reasons why your goldfishes fins are turning black, some are health related that need immediate attention and others are not so this article should give you some insight.

Why Are My Goldfish Fins Turning Black?

Goldfish are some pretty neat creatures no doubt, and there are actually quite a few different kinds of them. Generally speaking, they tend to be fairly easy to take care of, but there are some things that you must watch out for.

Yes, these fish are named goldfish, but they can change colors. Sometimes they change color naturally, and sometimes it happens due to environmental causes, such as aquarium conditions. Let’s talk about why your goldfish fins are turning black, if it makes a difference, and if necessary, what you can do about it.

1. A Natural Fin Color Change

First off, goldfish will change color depending on their location and surroundings, especially when lighting is concerned. Goldfish have different types of cells located within their scales that produce different colors. Some of these cells produce melanin, the primary compound which causes dark skin colors in people.

What is interesting to note is that goldfish that live in fairly dark environments with dull surroundings and little or no lighting often change to a blackish color. Some goldfish only suffer from their fins changing black, while there are more extreme cases where the whole fish turns black. Now, this is not a health issue per say and it really won’t affect your goldfish.

Heck, your goldfish probably won’t even notice. However, although it is not a health detriment, you might mind the color change. The simple solution here is adding some brightness to your goldfish tank. Increase the lighting and add some colorful decorations. This should take care of black fins, and after several weeks, they should return to their original color.

2. Ammonia Burns

Another well-known cause of goldfish fins turning black is that of the ammonia burn. Ammonia is lethal to fish in even small quantities. It poisons them, it suffocates them, and it will kill them quite quickly if not taken care of.

Black fins on your goldfish are an early warning sign that the ammonia levels in your aquarium are way too high. In fact, any ammonia is too much. If your goldfish fins are turning black, you should test for ammonia right away.

What is interesting here is that the black color actually signifies that the ammonia has caused a skin infection, one that is actually starting to heal. It may sound weird that black fins are a sign of healing, but it can go either way.

They might heal, or the high levels of ammonia might continue to wreak havoc on your fish. Either way, you need to make sure to take care of the ammonia problem.

High levels of ammonia are caused by uneaten food that is decaying, decaying plant matter, and fish waste. In other words, high levels of ammonia in any fish tank are more or less a result of improper tank care. You need to clean your tank on a regular basis and remove all debris. At the same time, having a biological filter that works well is a big bonus too. Biological filtration units take care of ammonia with surprising efficiency (more on lowering ammonia levels over at this article).

On this same note, tanks that are too small, aren’t cleaned well, and have a high level of toxins can also cause goldfish discoloration, even those black fins we are talking about.

The best solution is to get a larger tank, get a good multi-stage filter, and make sure that you always clean the tank. Besides discoloration, a dirty and not well maintained tank can have other serious health effects as well.

3. Disease

Although it is rare for goldfish fins to turn black due to disease, it is possible. There is a type of parasite that can infest fish tanks, a parasite that usually hitches a ride with snails.

So, if you have a goldfish with fins that are turning black, and you have snails in the tank, chances are that this parasite is the cause. This parasite lays burrows under the skin of your fish, it then lays eggs, followed by the creation of a black and hard cyst, thus the black fins.

If you want to get rid of the black fins, the parasites, and have things go back to normal, removing the snails from the tank should do the trick. It might take a month or two for this solution to take effect, but it will work.

Also, if the problem appears very severe, using some kind of aquatic parasite treatment will work as well. It will take care of the problem faster, but it will cost some money.

If you goldfish is swimming upside down then this post will explain why.


As you can see, black goldfish fins can be caused by various things, the most common of which is low lighting. However, ammonia and other toxins are always problems, to make sure to test for them and to keep your tank clean and well maintained. If you have snails, it’s probably a parasite causing the color change, so take care of that if needed.