Hepper is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

Why Is My Goldfish Turning Red? Reasons & FAQs

Lindsey Stanton Profile Picture

By Lindsey Stanton

gold fish

When a goldfish turns red, it isn’t usually a good thing. While some species are reddish, no goldfish should suddenly turn red. This is almost always a sign of a disease or some similar problem. Exactly what disease is arguable, though. There are a few different things that can cause a red color on a goldfish.

In this article, we’ll discuss some of those issues and their treatments.aquarium plant divider

The 2 Reasons Why Your Goldfish Is Turning Red

1. Red Pests

fish food in pond
Photo credit: Pixabay

Red pests are some of the most common causes of a goldfish turning red. This illness is also called pond pests and is caused by a bacterial infection of the bacterium cyprinicida. When infected with this bacteria, blood red patches will appear on the body of the goldfish.

On lighter color varieties, this is usually quite easy to see. However, it can be hard to detect on fish like the black moor, as the highly pigmented skin. Other signs include body mucus and clamped fins.

Typically, a healthy fish cannot be affected by this bacterium. Poor water conditions weaken the fish and then the opportunist disease sets in. For that reason, this issue almost always means that the water conditions need to be improved.

When you notice your fish has red pests, you should make a 50% water change immediately. You should also check the filter, as a clogged filter can severely upset the water quality. You may also want to check for anything that could be polluting the water, such as dead fish.

The pH and ammonia levels should also be checked.

As you are changing the water, add non-iodized aquarium salt. Methylene Blue can also be used as a treatment.

2. Ammonia Poisoning

Lionhead goldfish died due to poor water quality_Zay Nyi Nyi_shutterstock

Ammonia is a common killer of fish. This usually occurs as soon as the tank is established. If you put too many fish into a single tank, then this can happen as well. Filter failures can also cause elevated ammonia. Water testing will help you confirm if this is what is wrong with your fish.

Ammonia poisoning doesn’t really happen because the fish overdose on ammonia. Instead, the elevated ammonia offsets the nitrogen cycle due to the elevated pH levels. Preferably, ammonia levels should be kept at nearly zero.

This disease can occur suddenly or over a period of days. A tall-tale sign is a reddish-color appearing on their gills. They may also look like they’re struggling to breathe. Eventually, this will lead to death. The fish will slowly become more lethargic and lose their appetites.

As the poisoning continues, the fish’s skin will deteriorate, which causes red streaks and bloody patches.

The only real way to treat this problem is to fix the ammonia content. You will need a test kit and to do regular water changes. You should lower the water pH to as close to neutral as possible. You can do this relatively easily by doing a 50% water change. You should then continue to do water changes regularly.

You should not just change all the water. This will stress out the fish and can cause death when they’re this sick. If the fish appears particularly distressed, then you can use a chemical pH product to correct it. However, these often cause more harm than good, so you should only use them when absolutely necessary.aquarium plant divider

How Big of a Tank Does a Goldfish Need?

Usually, goldfish develop red spots and splotches because of poor water quality. Even if it ends up being a bacterial infection, it is likely the water quality that caused the infection in the first place.

Usually, water quality goes south because the fish are not kept in a larger enough tank. Goldfish need more room than most people think they do. They are not designed to be put in a bowl. In fact, very few fish are okay with being kept in a bowl.

Fancy goldfish need at least a 20-gallon tank. If you have more than one goldfish, you will need to add at least 10 more gallons to your tank size per individual. The bigger, the better.

Just because the fish have room to swim does not mean that the tank is big enough. That is not what dictates how much room a fish need. Instead, the tank needs to be so large to hold enough water to dilute the ammonia that the fish produce. Goldfish produce a lot of waste, so they need to be kept in a large tank to dilute this water.

If you're new to the world of goldfish or are an experienced goldfish keeper that loves to learn more, we recommend you check out our best-selling book, The Truth About Goldfish, on Amazon.

From diagnosing illnesses and providing correct treatments to ensuring your goldies are happy with their setup and your maintenance, this book brings our blog to life in color and will help you to be the best goldfishkeeper you can be. 

aquarium plant divider

Now What?

If you notice your goldfish turning red, then you should begin improving the quality of the water in the tank. A 50% water change is called for. You should do two 50% water changes every day until the water quality is pristine. You should also add aquarium salt, which will particularly help if they have a bacterial infection.

In the meantime, you also need to figure out why the water quality was poor, to begin with. You will likely need a bigger tank, or to perform more water changes. You can technically keep a fish in a smaller tank than they need, but you will need to do daily water changes.

You may also want to look into cycling your tank, which helps the natural bacteria in the tank remove the ammonia from the water naturally.

See Also:

Featured Photo credit: Washu, Pixabay

Related Articles

Further Reading

Vet Articles

Latest Vet Answers

The latest veterinarians' answers to questions from our database