What Causes Red Slime Algae in Salt Water Fish Tanks?

Red algae is slimy, can be a range of colors and is not a true algae. For most aquarists, red algae is just a headache.

    identification

    • According to Berkeley University, red algae is actually colonial, photosynthetic bacteria over 3.5 billion years old. Red algae, or cyanobacteria, is commonly referred to as slime algae. It can overwhelm an aquarium quickly if steps are not taken to fix the causes.

    Light

    • One of the prime causes of red algae is light with too yellow a spectrum; another is leaving the lights on too long during the day. If the algae gets bad, try reducing the time the lights are on or replacing your daylight bulbs with actinics.

    Nitrates

    • Nitrates are a common problem in marine aquariums. They can be caused by old filter media, like sponges, which harbor other helpful bacteria of the nitrogen cycle. A water change or replacement of filter media should fix this.

    Phosphates

    • Phosphates are present in most city water and can be a major problem in aquariums. Cyanobacteria love phosphates, as most plants do (phosphates are a fertilizer). To fix this, use only reverse osmosis or distilled water when doing water changes.

    Warning

    • A red slime algae bloom is often a sign that the tank has not fully cycled. According to encarta, nitrates become very high as the nitrogen cycle (waste/ammonia/nitrite/nitrate/nitrogen gas) bacteria take hold. Do not add more fish to the aquarium during this time because they will not survive.