Can Fish Tanks Cause Mold?

Can Fish Tanks Cause Mold?

Here are the causes of molds in a fish tank. We have also added the types of molds, and DIY methods to get rid of them.

Can Fish Tanks Cause Mold? Various types of molds can grow in a fish tank. The area of mold shows dark brown to black color, these are unhealthy and lethal for the life of fish. In some cases, they cause syndromes and allergies, and fish goes through the treatment process. The mold lies in the bottom and sides of the tank, they are contagious in all forms, and the tank itself is responsible for their generation and growth.

Can Fish Tanks Cause Mold?

The identification of the mold layer is casual in a fish tank. The color is usually green or brown, and the texture is sticky and greasy for all possible reasons; its color may vary with the mold type. 

Causes of mold in a fish tank

Mold in a fish tank is caused by the decomposition of food, extra feed, decorative material, lack of cleanliness, low quality of water, filtration process, cloudy water, nutrient imbalance, lack of carbon dioxide, and light deficiency.

Decomposition of food

The excessive amount of feed in the tank starts accumulating in the sides and bottom of the tank. The leftover food turns into toxic things like molds. Multiple types of molds enhance due to this impact in the aquarium.

The food chunks and other specific foods remain there, and then decomposing starts. The fish do not eat such food, and it generates a smell in the fish tank. Ultimately the complete decomposition of food increases the number of phosphates and nitrates due to several materials.

The mold makes a layer at the bottom and then at the sides of the glass tank. You can remove the decomposing food items, and you can see it through the glass screen that it is flourishing every day. 

Extra feed 

The food of the fish contains all types of nutrients for a healthy lifestyle. Sometimes people find out that their fish are becoming healthy with every passing day.

It increases the urge to provide them excessively every day. Initially, the fish takes the feed as a joy fact, but latterly they start avoiding it.

The fish takes two to three meals a day, and the extra food accumulates in the tank. The bottom of the fish tank becomes overloaded, and it generates a sense of suffocation.

 The extra food makes phosphorus fumes, and the fish inhales that which is extremely toxic for their health. This mold originates due to these fumes and an unhealthy environment.  

Decorative material

People add different plants and stones in their aquarium to make it more appealing. These things are excellent for the fish tank in a few cases, but the longer they are in the tank it damages excessively.

The plants inside the aquarium require replacement after a few weeks, and some people do not pay attention to them. The plants start drying, and the oxygenation process gets slow. 

The toxic environment reaches a level where you can see brown to black mold on the surface area and corners. It is the due presence of harmful materials in the water that increases the amount of ammonia.

The fish feels sick in this environment, and it is lethal for them. Some of them die, and a few get infectious disorders. 

Lack of cleanliness

Lack of cleaning leads to multiple problems that include molds. Fish tanks need cleaning and replacement of water now and then, but few people leave it as it is for months. The reason can be anything, but the water gets dirty.

The algae and fungi start prevailing in the fish tank. Initially, the layering is small, and it is easily removable, but with time the tank becomes polluted. The plants and food items reach the worst conditions.

They produce all the toxic substances like nitrates and ammonia, and molds form. These types of fungi are black, and they look dirty. This can turn your fish tank green very fast.

Bad quality of water

Water is a source of food and oxygen for the tiny creatures in the water tank. People replace the water of the tank to keep the fish safe and secure all the time. They do not follow the precise guidelines for changing water around the fish.

Most people use fresh and potable water for their aquarium. It contains several phosphates and phosphoric acid. It leads to molds immediately, and it is one of the most suitable environments for them.

The whole fish tank gets filthy, and the fish starts feeling suffocated. Some of the tiny creatures die due to eating these molds. They find this as food material, and when they eat this toxic substance, they get kidney failure, and fish dies. 

Filtration process

Filtration of tank water is a vast process which includes the addition of various chemical. Some people de-chlorine the water, and they add an excessive amount of chlorine. The filters of the aquarium become active at that time.

They encompass the number of chemicals in them, and the chlorine increases the generation of tank molds. The amount reaches a drastically harmful level.

The only solution leaves to replace the water. The cleaning of the tank comprises the addition of sea salt that removes few toxins, but it is also an instigating factor for all fungi.

Cloudy water

The addition of excessive feed in the water of the tank makes it cloudy and blurry. The display becomes so blur for the fish that they go through injures and physical accidents with the plants.

The cloud water not only contains nutrient-rich food, but it also has toxic substances. The mold becomes active in such an environment, and they increase excessively.

The sides of the aquarium get filled with fungi. The initial stage is the presence of green Algae, and then it turns into brown sticky material.

Eventually, you can see black molds all around the tank, and few of them are removable. Several molds are so toxic that the only solution is changing the tank. 

Nutrient imbalance

The water inside the aquarium is a nutrient source for the fish, and the imbalance of the essential nutrients allows the production of these bad things. 

The excessive amount doesn’t have to bring the molds into life, and the lack of necessities generates the harmful layers. They cover the corners and sides of the tank, and the whole sight becomes ugly. 

Lack of carbon dioxide

Carbon dioxide is an essential thing for the plants inside the fish tank. The dirty water leads to a deficiency of carbon dioxide and other healthy gases.

The plants lack their survival, and they stop the process of oxygenation. The environment is suitable for the generation and growth of fungi and algae.

The suffocation promotes the whole process, and fish feels allergies and irritation. The unhealthy grasping of air inside the gills promotes ulcers, and the problems are so severe sometimes that the tiny things start dying. 


Light is a good source for the growth of all types of molds. It does not matter either it is artificial light of sunlight, the molds grow. Some people place the aquariums under sunlight or another light source.

The constant embarking of photons on the tank’s water makes it vulnerable. The fungi generate at the top corners because light has more impact at these corners. The only solution is the movement of the tank from the light source. 

How do I get rid of mold in my fish tank?

Less time for feeding

  1. Control the time of feed to the fish in the water house. The maximum time should be fifteen minutes.
  2. Do not drop an excessive amount of grains and other food items.
  3. Save the water from the cloudy effect of dirt and leftover food. 

Change of water

Dirty water promotes the growth of fungi and algae. Black fungi immensely grow in this type of environment. Replace the tank’s liquid with fresh water and make it a safe and healthy place. 


These are a fantastic solution for keeping the tank free from all types of molds. The antifungals remove all of the fungi and keep the water clean. You should not add an excessive amount of these antifungals.

Isolate the fish in some other tank and then add these medications. Leave it for at least 30 minutes inside the tank, replace this water with new and freshwater. Purify the water and then add it inside the place, but the fish back in their aquarium, they are cost-effective and beneficial. 

Use Epsom Salt

Sea salt is also known as Epsom salt, and it is a good remedy for cleaning the aquarium. Add two to three tablespoon of the salt to the tank and leave it for few minutes. Never exceed the time from fifteen minutes, or this irritates the fish’s skin.

Quarantining the tiny things in another tank and then cleaning is another best option. Buy this salt from the aquarium stores, and it is lighter on the budget. 

Types of molds in a fish tank

Types of molds Reasons Solution
Black fungi It appears due to the excessive amount of leftover food. The enhanced level of phosphates also instigates its growth. Remove the toxic food materials and make sure the water is not containing too many phosphates.
Green fungus The poor condition of water causes the origination of green fungi. A nutrient deficiency promotes its growth. Replace the water regularly or every three days. Provide several food nutrients to the fish.
Black beard algae It is also known as red algae, and it originates due to a high level of phosphates. Remove and replace the water in the tank. Clean the siphon inside the tank and purify the fresh water before adding it to the aquarium.
White fungi These appear due to substandard water, and the infected food makes it worse. The open wounds of fish also increase the generation of fungi. Replacement of water and infected food items cleans the fish tank from the mold. Treat the fish with dangerous wounds, or it makes the tank filthy.
Algae Water, nutrients, and light are the source for the growth of algae in the aquarium. Reduce the number of following materials and keep the tank at a moderate level.

Are molds in a fish tank harmful to fish?

The molds influence the health of the fish. It leads to an enormous number of syndromes. They produce allergens and irritants that cause allergies and other such diseases. Some of the substances are toxic, and they are lethal for the fish.

The fish have the water of the tank for them that is the oxygen source. They inhale the substances and spore through the process of breathing.

The materials generate sensitive reactions inside the body, and it starts appearing on their skins. The excretion of high-level nitrates and ammonia kills the fish within minutes.

Related Articles:

Can you store a fish tank outside in cold?

How to make a homemade fish tank lid?

How to fix a cracked aquarium bottom?

Best aquarium sea salt for marine fish tanks