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Aquamaniacs Problem Profile -- Blue Green Algae

Name: Blue Green Algae, Cyanobacteria or BGA
Type: Algal and bacterial
Agent: Cyanobacteria
Difficulty: Easy to moderate
Distribution: Substrate, decor and plants
Symptoms: Fast growing, unsightly slimy sheets of black, brown or greenish blue colored algae. A musty smell is typically noticed when the tank lid is raised.
Treatments: The best approach to bringing BGA under control is to apply the following corrective actions in order:

Quote:

Things that must be done:
1. Remove as much visible BGA as possible via water change (up to 50%) and manual removal.
2. Clean filter media and remove filter carbon (GAC)
3. Assure ample water circulation and filtration. A filter turnover rate of at least 4 to 5 times per hour is a good general minimum. When fighting BGA, added circulation from an airstone, bubble curtain or secondary filter must be deployed.
4. Discontinue the use of buffering agents that contain phosphates. Check your label or manufacturer’s website.

Things that can/should be done after the things that must be done:
1. Add phosphate absorbing beads or pads to the filter.
2. Add CO2 injection to a planted tank. This will lower pH and help kick the plants into high gear.
3. Add KNO3 in the form of liquid fertilizer to planted tanks only. Maintain NO3 levels at 5 to 10 ppm.

Things that help temporarily. Use only after everything listed above has been done:
1) Do a three-day blackout with a trash bag or dark blanket, so that no light gets in the tank at all. Remove CO2 injection during blackout.
Or
2) Remove fish and apply Maracyn, or Kanamycin as per package directions.

Prophylaxis: Maintain water quality and stability. Be careful not to overfeed and do not add fertilizers or buffers that contain phosphate. Planted tanks, make sure there is measurable NO3 -- 5 to 10 ppm is ideal.
Mortality: N/A
References:

Notes: In order to defeat an opportunistic organism, it is important to understand its requirements. Since BGA has the ability to "fix" nitrogen (remove it from the air), it makes for a perfect bio-fertilizer for farming applications in emerging parts of the world. The production of BGA based bio-fertilizer calls for a few inches of resting water in a very sunny location. Soil (as substrate), BGA flakes (as inoculum), super phosphate (as food) and lime (to raise pH) are then added. The algae is then dried and harvested for fertilizer or used as more inoculum. Depriving BGA of as many of its requirements as possible is the best approach to removing it from an aquarium.

There are no known fish or shrimp that will consume BGA. Some fish and snails will nibble on it as it begins to die back.