How to Remove Brown Algae From Your Aquarium

brown algae in aquariums

Illustration: © The Spruce, 2018

If you've owned a fish tank, you're probably familiar with the dreaded brown mossy substance that can quickly take over your fish's home. It's brown algae and is especially common in new aquariums, which may cause concern for people new to owning fish.

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

The good news is that this issue is pretty easy to clean up. It's 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 a Brown Algae Problem

Brown algae (also called gravel algae or silica algae) begin as brown patches on the gravel and/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.

Unlike blue-green slime algae, it does not come off in large slimy sheets. These patches almost look furry. While they won't hurt your fish, the algae will cloud the water and generally make your tank look less appealing. It's also a sign that the chemistry of your tank isn't at an optimum balance.

Causes Brown Algae

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

  • Excess silicates and nitrates
  • Inadequate light
  • An abundance of nutrients
  • Low oxygen levels

Silicates can build up through tap water that is high in silicic acid. It can also leach from some types of substrates. In addition to tap water, nitrates can build up from uneaten food, dead material, or an overstocked environment. Along with lighting, these should be your biggest concerns. Taking care of them should balance the tank's nutrient and oxygen levels.

How to Remove Brown Algae

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

  1. Wipe off all surfaces and vacuum the gravel well.
  2. Use silicate adsorbing resin in the filter.
  3. Increase the lighting so the tank gets 6 to 8 hours a day.
  4. Stock a plecostomus or several otocinclus 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 can't grow back as quickly. You should wipe off any tank decoration 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.

Some sucker-mouth catfish—most notably, plecostomus and otocinclus—will readily eat brown algae. If the problem is due to high silicates in the water, and the brown algae persist, a special silicate absorbing resin can be used in the filter.

How to Prevent Brown Algae 

As with any algae, keeping the tank clean and performing regular water changes are the best preventative measures. Ensure that your aquarium maintenance involves these four things:

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.