Why your aquarium gravel turns brown and what to do

Last Updated on January 18, 2021 by cmoarz

If you have an aquarium, you must have noticed the brown color developing on the gravel. And this is quite a turn off because it does not look pleasant, and it also creates a dull environment for the fish. But what is it, and why does it turn blue?

The brown color that you see on the gravel and glass is called silica algae. It is also referred to as brown algae because it starts as brown patches in different parts of the aquarium glass. And if you ignore it in the initial stages, it keeps growing bigger and begins to develop into a thin layer of brown coating over the glass or gravel’s surface.

Brown algae growth is a common problem faced by any new aquarists. And even if you are familiar with aquariums, you still face the same problem when you purchase a new one. But it is not something that you should be alarmed with because you can easily clean them off. And it helps a lot if you know the cause of the algal growth so that you can avoid them in the future. So here is what you need to know about brown algae.

What are the different brown algae?

Brown algae (true brown algae) is part of the class Phaeophyceae, a group consisting of many multi-cellular algae. And this type of algae also includes different kinds of seaweed found in cold waters, such as kelp. However, the algae that grow in your aquarium is not of this type.

There is another type of algae called Golden Algae from the class Chrysophyceae. It is a large group of algae that are yellow or brown and generally found in freshwater bodies. It acts as an essential source of food for many organisms in the water. These are single-cell organisms with a cellulose cell-like in plants, and you can find them suspended on water columns. But this is also not the type of brown algae you find in your aquarium.

What is silica and brown silica?

Silica is an abundant element found in the environment. It results from combining silicon with oxygen in the natural state, and it is found abundantly in the water bodies. And there are organisms called diatoms that create a protective clamshell using the silica in the water. So brown algae are the other name for the diatoms.

The diatoms belong to Bacillariophyceae class, and these are the algae that make it to your aquarium through saltwater or freshwater. They are unicellular organisms that can thrive as solitary cells or as colonies.

However, Brown algae do not have any harmful effects on the fish as long as you keep them under control. There are fishes that like to eat the algae, but the algae’s growth is not ideal for your aquarium because it makes the aquarium look bad with dirty brown patches.

The cause of brown algae

Brown algae growth is typical in new aquariums. And one of the causes is keeping the aquarium in dark places with little light. All the algae and plants in the tank require light for growth and compete with the diatoms for nutrients. To avoid this, try and keep your aquarium where there is ample light to feed the plants and algae.

When you see brown algae in your tank, it is also a sign that there is a problem with the water chemistry, and it is not in balance. Therefore, after ensuring that there is enough light for the aquarium, the next thing to do is change the water and keep it fresh.

Most aquariums use tap water. And tap water is known to have high silicic acid content. And in many cases, the silica can leach from the substrates that you use. So if you notice brown algae growth and find out that the cause of the build-up is due to high silica in the water, you can get a silica-absorbing resin for the filter in the tank, and this should fix the problem.

There is another possibility for the brown algae growth in your tank. The nitrates can build up by feeding on the diatoms and uneaten food, and dead material. So, in this case, changing the water frequently can solve the issue.

How to remove brown algae?

Removing brown algae is not as complicated as you think. They are easy to clean because all it needs is a rub. The brown algae do not stick firmly, so it does not take a lot of effort to remove them. All you have to do is wipe them off from the glass, gravel, or any other tank material with brown algae. And you can finish it up by vacuuming.

However, removing brown algae from the gravel is the trickiest part. So the best option is to vacuum the stones instead of wiping them. And there is another option that is an ideal choice for keeping your aquarium free of brown algae. Suckerfish eats brown algae, and keeping a few of them will do the job for you. It will save your time and effort and keep the aquarium nice and clean.

How to prevent brown algae growth

There are a few things you can try to keep your aquarium free from brown algae. And they are;

  • Increasing the lighting in your aquarium so that it gets at least eight hours of ample light
  • Keeping fresh live plants that can eliminate brown algae
  • Regular partial water changing

You can try these preventive measures so that it restricts the brown algae growth. However, it is worth mentioning that all these preventive measures do not guarantee that the brown algae will not grow. Despite regular maintenance and care, brown algae can still grow and is a common problem. Nonetheless, maintenance and preventive measures do minimize the problem. So try and follow them and keep an eye on the sudden and rapid growth of brown algae because if ignored, it can cause serious problems.


Owner of AquariumGravel.com and also owner of actual Aquarium Gravel believe it or not! ;). Setting up beautiful aquarium sceneries and habitats since I was very young. Enjoy!

2 thoughts on “Why your aquarium gravel turns brown and what to do”

Comments are closed.