What Kind of Mold Is in Fish Tanks?

Mold and algae spores are present in most aquariums. Fish and plant waste provide nutrients that the spores need to multiply, producing residue on glass, plants and fish tank ornaments. Suspected fish tank mold below the water's surface is actually algae, but many people mistakenly refer to it as a type of mold. Accurate identification of mold and algae enables you to implement an effective method of removal. Algae-eating fish help keep some types of tank bloom under control.

  1. Mold

    • Bacterial blooms inside your aquarium hood and areas above the water line are usually mold caused by damp conditions and condensation. Some algal spores are able to survive and multiply in these places, but regular cleaning is enough to keep them under control.

    Diatoms

    • Patches of soft brown fluffy growths in a freshwater aquarium are diatom organisms from excessive silicates or insufficient tank lighting. This type of brown algae are often mistaken for mold. Wipe affected areas clean and add extra light to the aquarium so the diatoms can not take hold and re-establish a colony.

    Cyanobacteria

    • Unhealthy water quality encourages blue-green slime to grow, quickly covering everything in your tank and smothering plants. The organism responsible is cyanobacteria and it is extremely difficult to remove. A commercial preparation containing erythromycin phosphate is effective, but affects your biological filter's efficiency, so check ammonia and nitrate levels after use.

    Spot Algae

    • Bright green spot algae on aquarium glass that feel hard and crisp are a symptom of too much light. Gently scrub acrylic tanks with a soft cloth or scrape glass with an abrasive tool.

    Beard Algae

    • Plant leaves covered in bright green fuzzy patches may look like they have a mold infestation in the early stages of a beard algae outbreak. Beard algae take on a bushy texture and grow quickly, ceasing to look like mold. An anti-algae treatment is the only way to combat beard algae because manual removal damages plant leaves.

    Brush Algae

    • Short black tufts growing on large leafed plants are brush algae, or audouinella. They are easily confused with mold in your aquarium. Fish called Siamese algae eaters control brush algae effectively, but in extreme cases an algaecide containing copper may be useful.

    Staghorn Algae

    • Single strands of gray-green residue near the water's surface and on equipment is staghorn algae. Left unchecked, they grow into the shape of deer antlers and are difficult to eradicate by hand. Remove affected items and scrub everything clean. Soak equipment in an anti-algae solution and rinse before returning it to your aquarium.

    Hair Algae

    • Coarse clumps of green algae around your filter and plants are likely to be hair algae, and resemble tank mold in its early stages. Hair algae rarely grow longer than 2 inches and manual removal is essential so that they do not damage plants and embed into the substrate.

    Thread Algae

    • Foot-long strands of dark green fine algal filaments in your aquarium are thread algae caused by too much iron in the water. Scrub thread algae at the base with a small brush as soon as you see a bloom. Improve your water quality to prevent further growth.