Skip to Content

5 Reasons Your Fish Is Shedding Its Slime Coat!

There have been a number of surges in the popularity of the fish keeping hobby over the last decade and we are currently seeing another boom in the hobby.

This has caused a number of people to get involved in fish keeping recently with there currently being more people than ever getting their very first tank.

As you can probably guess, with there being so many beginners out there, we are seeing a surge in questions from people that are having problems with their fish and looking for ways they can help their fish.

One question that a number of people have been asking recently is about their pet fish shedding its slime coat.

For the most part, the mucus coat on a fish is important for the health of the fish so if it is shedding the slime coat, then there is usually a potentially serious problem with the fish that needs treating quickly.

This is why we have decided to publish this article going over the most common problems that can cause fish to shed their slim coat.

Our hope is that we will be able to help our readers get a better idea of the potential causes of the issue as well as what they can do to treat the problem.

Why Your Fish Is Shedding Its Slime Coat!

Here is our short list of the more common problems that can cause your fish to shed its slime coat:-

  • Velvet!
  • High Levels Of Ammonia!
  • Salt Levels!
  • Water Temperature!
  • Mucus Overproduction!

Some issues above may be occurring in your tank at the same time and the first four causes can result in mucus overproduction but there are many other causes of mucus overproduction too but more on that later.


The velvet parasite can be common within the fish keeping community and if the problem is not treat quickly, in its later stages it can cause serious issues with the skin and scales of your fish.

In very bad cases, they will physically peel off the fish and this can give the impression that the fish is shedding its slime coat.

In most cases, you will usually have plenty of notice prior to this happening as velvet is an obvious problem in fish that can easily be noticed due to the chances on the scales of your pet fish.

In many cases, simply lowering the light exposure to your fish tank will be enough to deal with the velvet parasite quickly but if the scales and skin of your fish have already started to peel then it is often too late to save the fish.

High Levels Of Ammonia!

High ammonia levels can be a serious issue for any fish and can cause a number of problems, one of which is the shedding of the slime coat.

If you notice that your fish are starting to shed their slime coat and you have high ammonia levels in your tank then it is important that you act quickly as this is a serious problem that needs addressing.

One of the best ways to lower ammonia levels quickly is to do a partial water change of between 15% and 25% and this will also help to remove any other potential toxins that may be in the water.

If possible, you should do a quick test with a water test kit to get a better idea of the condition of your water parameters and confirm if ammonia levels are the problem.

Although high ammonia levels can cause your fish to shed its mucus coat, it is usually when the ammonia levels get very bad so you will usually be able to avoid this with regular water changes in your tank.

Salt Levels!

The level of salt in your tank can also have an effect on the slime coat of your fish with salt levels being too high or too low being able to cause the shedding effect.

This is not specific to salt water tanks either and in many cases, people have started to add small amounts of aquarium salt to a freshwater tank.

Although this can offer some benefits, we really don’t recommend it if you are new to the fish keeping hobby as it can easily cause a number of problems with your tank.

For the most part, avoiding the use of aquarium salt in a fresh water tank will be enough to prevent you from having this problem.

In a salt water tank, using a salinity test kit should be able to give you a good idea if your salt levels are out of the recommended levels for your fish and then you can go about fixing the problem.

Water Temperature!

Although rare, some fish can have issues with shedding their slime coat due to the water temperature in their aquarium being too high.

Many community tanks have to use a temperature balancing system as it is difficult to offer the correct temperature range for all tank mates in a community tank.

This can often result in fish living in a tank that is slightly out of their recommended temperature range and causing problems.

If you do notice that one of your fish is shedding its slime coat then quickly checking the recommended temperature requirements for the species and making sure that your tank water temperature is in range may fix the problem.

Mucus Overproduction!

There are a large number of potential causes of mucus overproduction in fish.

This does not actually cause your fish to shed its mucus or slime coat but just gives the impression of it due to there being too much mucus on the fish.

You will often see areas of the body of your fish that have excess slime on them making it obvious that this is the problem.

If you watch your fish long enough, this excess mucus will then usually fall off the fish giving the impression that the fish is shedding its slime.

Just because your fish is not shedding its slime coat does not mean that the fish is safe though.

Some of the causes of mucus overproduction in fish can end up developing into serious problems so you really do have to work on finding the problem and fixing it quickly.