What Is The Black Mold in My Fish Tank

The black mold in your fish tank is either algae or mold. While it looks like mold, it is most probably black algae. In this post, you will learn everything important you need to know about black algae and black mold and how to get rid of whichever one of them is giving you sleepless nights.

Black Algae in Fish Tank

As I mentioned above, the thing that looks like black mold in your tank is most probably black algae. Black algae are not the easiest algae to eliminate from a fish tank. However, it can be eliminated. Now that you have an idea of what it could be, you should endeavor to act as soon as possible before it spreads throughout your tank and becomes harder to remove. 

The Conditions That Aid the Growth of Black Algae

Before I share with you tips on how to remove black algae, I believe it is important for me to tell you the conditions that aid the growth of algae. Because if you get rid of the algae before destroying the conditions that make it easy for them to grow, they will grow again. So getting rid of algae before making it near impossible for them to grow is not really clever. 

Below are the conditions that aid the growth of black algae:

  • Lack of frequent partial water changes: In case you do not change a fraction of your tank water every week, nitrates will accumulate in your tank. And high nitrates almost always lead to growth in algae because algae feed on nitrates
  • Late replacement of a fluorescent bulb: If you are using a fluorescent bulb as a light source, you should replace it every five months. This is because, after five months, fluorescent bulbs start emitting a different kind of light that favors algae growth by enabling them to generate energy via photosynthesis. Therefore, to prevent an algal outbreak, you should change your fluorescent bulb early or switch to a LED anti-algae light.
  • Delayed removal of fallen leaves and dead plants: If you do not quickly remove fallen leaves and dead plants, they will start decaying in the tank. As they decay, they will release organic waste into the aquarium leading to algae growth.
  • Overfeeding fish: When you overfeed fish, they release more waste into the aquarium. This increases the level of organic waste and may make your filter struggle to keep the water clean. And when a filter struggles to do its job, the conditions become very conducive for an algae outbreak.
  • Overstocking fish: Overstocking just like overfeeding contributes to algae outbreaks by increasing the quantity of organic waste in aquarium water and making filter systems struggle to do their job. 
  • Uneaten food: When your fish does not eat all the food you drop for it, the remaining food will start decaying and this will lead to algae growth.

As you can see above, several things can trigger the growth of black algae in a fish tank. Addressing these pro-algae conditions is the best way to make algal outbreaks less likely.

How to Get Rid of Black Algae

As stated earlier, black algae are not the easiest algae to eliminate from a fish tank. However, there are several chemical and natural methods you can use to eliminate them. 

How to get rid of algae and prevent outbreaks: 

  • Use an aquarium vacuum: There are many aquarium vacuum models available on Amazon. By getting one of them, you can instantly eliminate all the black algae in your tank. You can also use it to eliminate debris and waste making future algae outbreaks less likely.
  • Use algae eating fish: You can eliminate black algae in your tank and make it less likely for them to come back again by introducing algae-eating fish such as bristlenose plecos, catfish, pond loaches, and Siamese algae eaters. These fish like eating algae and will clean your tank very quickly. They will also eat any new algae and make it impossible for algae to re-emerge in your tank.
  • Use an algae-killing light: There are several LED UV lights on the market that can control algae. They are a bit expensive but they are very effective for killing and controlling bacteria and algae.
  • Feed fish less food: By feeding your fish less food, you will reduce the quantity of waste released by the fish and this will make algae outbreaks less likely.
  • Use a nitrate remover: Algae in fish tanks primarily feed on nitrates for survival. By using a quality nitrate remover, you can eliminate the food that algae rely on and eliminate them by making it difficult for them to survive. However, while nitrate removers are effective for eliminating algae and preventing algae outbreaks, they are chemicals and, therefore, they can negatively affect other tank inhabitants. You should only use them if you have tried natural methods without any success. 
  • Do regular tank maintenance: By doing regular tank maintenance and cleaning everything, you will make the conditions less conducive for algae to live and survive. 
  • Do frequent water changes: Doing frequent water changes is one of the best ways to eliminate algae and prevent algae outbreaks. This is because frequent water changes reduce the concentration of nitrates in water and, therefore, reduce the food that algae rely on to grow and multiply.

Most aquariums experience algae outbreaks. However, by using the methods above, you can eliminate algae and make algae growth less likely.

Black Mold in Fish Tank

As mentioned earlier, the thing looking like black mold in your tank is most probably black algae. However, there is also the chance that it could actually be black mold. When mold starts growing in your tank, you should take immediate action because the growth of mold is a sign that your tank hygiene is not right.

When the conditions for the growth of mold are perfect, black mold usually quickly start growing on fish, rocks, décor, and glass walls. They usually start by appearing slimy and green. But they can also be black. The growth of black mold is rare in fish tanks but it is possible. 

The Conditions That Aid the Growth of Black Mold

Below are the conditions that aid the growth of black mold: 

  • Poor tank cleanliness
  • Poor water quality
  • Poor filtration
  • Overfeeding 

The conditions above aid the growth of black mold because they increase waste in the water. Decomposing fish wounds, decomposing excrement, dead fish, dead plants, and decomposing wood also promote the growth of mold because they are a source of nourishment for mold.

How to Get Rid of Black Mold

As stated earlier, if you think you have black mold in your tank, you probably have a black algae problem as black mold is quite rare. However, if you really think your black mold problem is actually mold, below are the steps you should follow to get rid of it:

  • Do a deep clean: If you have mold then the culprit is most probably poor tank hygiene. Somehow something has made your tank very dirty. The best way to make a dirty fish tank clean is to do a deep clean. You should switch off every system in your tank and take it apart to scrub and scrape everything. You should then replace 75% of the water. This type of cleaning is not usually recommended because it eliminates beneficial bacteria but it is important if you want your tank to recover from a mold attack. 
  • Replace your filter: The fact that you think your tank has mold is an indicator that your filter is not working right. This is because mold can only grow in very dirty tanks. So replace your filter with a more powerful filter e.g. a canister filter. A more powerful filter will help to prevent your tank from becoming too dirty and conducive for black mold to grow.

Final Word

The black mold you see in your tank is most probably black algae. However, it could also actually be black mold. If it is black algae, you can remove it using a siphon, by cleaning your tank regularly, and by introducing algae-eating fish. If it is mold, the best way to remove it is by doing a deep clean of your tank and getting a more powerful filter system.

Black algae and black mold often grow in dirty or poorly maintained tanks. So try to maintain your tank frequently and to thoroughly clean it every three months. This will prevent them from growing in your tank.