How to Remove Brown Algae in Fish Tanks

Master algae prevention with effective cleaning and care

The Spruce

Brown patches on the gravel or glass of the tank are a kind of film known as Silica Algae or Brown Algae. Once established, it can rapidly coat most surfaces of the aquarium's interior with a thin, dark brown coating.

This problem is especially common in new aquariums, which may cause concern for people new to fish keeping. The good news is that this issue is pretty easy to clean up; for the most part, it can be wiped off the sides of the tank and vacuumed off gravel. Some species of fish are also natural brown algae cleaners. It is also relatively easy to stop brown algae from even growing in your aquarium if you know the cause. A few preventative measures will make your tank look great and algae-free.

True Brown Algae, belonging to the class Phaeophyceae, are a large group of multi-cellular algae that includes many seaweeds in cold marine waters, such as kelp. These are not the types of algae growing in your aquarium!

Also, the Golden Algae, Class Chrysophyceae, are a large group of yellow-brown algae found mostly in freshwater environments; they are an important food source in food web dynamics of freshwater ecosystems. They are single-celled organisms that have a cellulose cell wall just like a plant. Many are also flagellated—having a tail for propulsion—so they are normally found suspended in the water column. These Golden Algae are also not often found in the home aquarium.

However, there is another kind of algae that grows in aquatic environments; it appears brown, especially under artificial lighting in the aquarium setting. This is referred to in the aquarium trade as Brown Algae or Silica Algae.

In its natural state, silicon, a common element, combines with oxygen to form silica, a primary compound in sandstone, quartz, and glass. Many single-celled organisms use it for protective "clamshells"; these organisms are known as diatoms.

"Brown Algae" is the common name that refers to diatoms, Class Bacillariophyceae, that find their way into freshwater and saltwater home aquariums. Diatoms are unicellular organisms that can occur either as solitary cells or in colonies.

Like plants and other algaes, diatoms photosynthesize light into energy. Each species creates a unique opal-like crystalline covering around its cell wall; these appear almost like snowflakes and are quite beautiful under a microscope even though they function as substantial armored protection for the tiny organisms.

Planktonic forms in open water usually rely on turbulent churning of the upper water to keep them suspended. But most diatoms are non-motile, as their relatively heavy cell wall causes them to readily sink to the bottom, creating a thin film across the bottom of any aquatic environment.

Generally, Brown Algae diatoms won't harm your fish if they are kept under control. Some fish like to eat these diatoms and can help to clean up your tank, but Brown Algae is generally not good for the home aquarium environment.

Unlike blue-green algae that can come off in large slimy sheets, these diatoms don't stick together. But patches of diatoms will generally make your tank look less appealing.

Brown Algae commonly appears in newly set-up aquariums. Those kept in dark places are more likely to develop Brown Algae issues because plants and green algae that thrive in bright light compete for the nutrients diatoms use.

Brown Algae is also a sign that the water chemistry of your aquarium is not in optimal balance. After providing proper lighting, improving water quality should be your next concern. In general, you can look at a few main causes: excess silica or nitrate in the water or an abundance of nutrients.

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. If the problem is due to high silica in the water, and Brown Algae seems to persist, get a special silicate-absorbing resin for the tank's filter.

In addition to possibly being high in your tap water, the nitrates that feed diatoms can build up from uneaten food, dead material, or overstocking fish. Increasing water changes to remove nitrates will slow the growth of these diatoms.

As the diatoms are merely resting on the bottom, a Brown Algae issue is easy to clean up; no scrubbing is necessary. This type of algae does not adhere strongly to the tank surfaces and is easily wiped away. Just wipe off any tank decorations that may be affected, wipe off all surfaces inside the aquarium, and then vacuum the gravel.

The hardest removal part is usually getting it out of the gravel, but vacuuming the gravel with a siphon will quickly remove it. Vacuuming is important to ensure the algae will not grow back as quickly.

In a freshwater aquarium, you can add a sucker-mouth fish that will readily eat brown algae. Stock one plecostomus or several otocinclus catfish to do this job. In a saltwater aquarium, many species of fish and invertebrates are diatom grazers.

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 despite regular maintenance, especially in a newly established aquarium. Prompt attention to sudden algae growth will prevent more serious problems later on.