How to Remove Brown Algae From Your Aquarium

Prevention Measures for This Common Occurrence in New Fish Tanks

Brown algae in aquariums

Illustration: © The Spruce, 2018

If you have owned a fish tank, you are probably familiar with the dreaded brown substance that can quickly take over your fish's home. This problem is especially common in new aquariums, which may cause concern for people new to owning fish. Brown algae begins as brown patches on the gravel or glass of the tank. Once established, it can rapidly coat most surfaces of the aquarium with a thin, dark brown coating that is easily removed, for the most part.

In general, brown algae will not harm your fish if you keep it under control. Some fish do like to eat it and can help you clean up, though it is generally not good for the aquatic environment.

The good news is that this issue is pretty easy to clean up. It is also relatively easy to stop brown algae from growing in your aquarium if you know what causes it. A few preventative measures will have your tank looking great and algae-free.

Identifying Brown Algae

So what exactly is "Brown Algae"? There are several kinds of algae that grow in aquatic environments that may look brown. There are even some of the "Green Algae" that may have a brown appearance, depending on lighting.

True Brown Algae, comprising the Class Phaeophyceae, are a large group of multi-cellular algae, including many seaweeds in marine waters, such as kelp. These are not the algae that are growing in your aquarium!

The Golden-Brown Algae, Class Chrysophyceae, are a large group of algae found mostly in freshwater and are important in the food web dynamics in freshwater ecosystems. An important characteristic used to identify the class Chrysophyceae is the presence of a siliceous cyst. Many of these are flagellated and are normally found suspended in the water column.

The final group of brown colored algae includes the diatoms, Class Bacillariophyceae, which are unicellular organisms that can occur either as solitary cells or in colonies. Diatoms have two distinct shapes: radially symmetric (centric diatoms) or broadly bilaterally symmetric (pennate diatoms). The diatom has a cell wall made of silica. Most diatoms are non-motile, as their relatively dense cell walls cause them to readily sink to the bottom of the aquarium. Planktonic forms in open water usually rely on turbulent mixing of the upper water to keep them suspended.

Unlike blue-green algae that can be a problem in an aquarium, this type of algae does not come off in large slimy sheets. These patches of algae will not hurt your fish, but may cloud the water and generally make your tank look less appealing. It is also a sign that the water chemistry of your aquarium is not at an optimal balance.

Causes of Brown Algae

Brown algae is a common occurrence in a newly set up aquarium. Aquariums kept in dark places are also more likely to develop brown algae problems. In general, you can look at a few main causes: 

  • Excess silica and nitrate in the water
  • Inadequate light
  • An abundance of nutrients
  • Low oxygen levels

Silica can build up in the aquarium from tap water that is high in silicic acid. It can also leach from some types of substrates that you may be using, such as silica sand. In addition to possibly being high in your tap water, nitrate can build up from uneaten food, dead material, or an overstocked environment. Along with providing proper lighting, improving water quality should be your biggest concerns. If you check each of these potential causes, you should be able to balance the aquarium's nutrient and light levels.

How to Remove Brown Algae

A brown algae issue is easy to clean up and no real scrubbing is involved. The hardest part is usually getting it out of the gravel.

  • Wipe off all surfaces inside of the aquarium and vacuum the gravel.
  • Use silicate adsorbing resin in the filter if silica is in the tap water.
  • Increase the lighting so the tank gets at least 8 hours of light per day.
  • Stock a plecostomus or several otocinclus (algae eating sucker-mouth fish).

This type of algae does not adhere strongly to the tank surfaces and is easily wiped away. Vacuuming the gravel with a siphon will quickly remove coatings from the substrate. This is important to ensure the algae cannot grow back as quickly. You should wipe off any tank decorations that may be affected as well.

Increasing the lighting will inhibit regrowth of brown algae. As a new tank matures, brown algae are often eliminated naturally by plants and green algae competing for nutrients in the water, such as nitrite and nitrate.

Sucker-mouth fish—most notably, plecostomus and otocinclus—will readily eat brown algae. If the problem is due to high silica in the water, and the brown algae seem to persist, get a special silicate-absorbing resin for the tank's filter.

How to Prevent Brown Algae 

As with any algae, keeping the tank clean and performing regular partial water changes are the best preventative measures. The best maintenance measures are summed up simply:

Unfortunately, it is still possible to get algae in spite of regular maintenance, especially in a newly established aquarium. Prompt attention to sudden algae growth will prevent more serious problems.