Answer: We have a lot of Blue Green algae problems in the lakes here in Oregon (it is not even a true algae, rather modified bacteria; Cyanobacteria). I understand that the out breaks have differences from aquariums, but there are similarities too. I did research on this subject (including reading the local newspapers about treatment and control in our local lakes). Two points that were made several times are:

[1] Heat, high summer temperatures, and poor in flow and out flow of water seem to induce an outbreak. This also relates to the Redox Potential. Fresh water and good Redox potential (-300 mV) seems to play a large role (from my own research and other research articles I have read). In lakes this bloom will usually conside with poor inflow and outflow of water. This also causes a change in trace element content as well as Redox. This can then be applied to aquariums in that maintaining regular water changes, a GH over 100 ppm (for calcium and trace elements) as well as the correct Redox (UV Sterilization helps here too), will all work towards prevention and eradication of this problem.

[2] Nutrients, the amount of nitrogen based and phosphate nutrients need to be reduced.

As this relates to aquariums, I would increase circulation, clean and vacuum the bottom every other day, cover the aquarium from light for three days, reduce the temperature, consider UV Sterilization to kill free floating spores, and reduce the nutrient level.

CYANOBACTERIA BASICS;

Knowing more about this "algae" is important for eradication:

Cyanobacteria are from the phylum Cyanophyta of Bacteria that obtain their energy through photosynthesis. They are often still generally referred to as blue-green algae, although they are actually prokaryotes (organisms without a cell nucleus) like bacteria. Prokaryotes usually unicellular, although some are capable of forming cell groups called colonies. Individual Blue-Green Algae that make up these colonies will usually act independent of one another. Colonies are formed by organisms that remain attached following cell division, often through the help of a secreted slimy layer that we often see as slimy green mat in our aquariums. Cyanobacteria are the only known group of organisms that are able to reduce nitrogen and carbon in aerobic conditions. The water-oxidizing photosynthesis is accomplished by coupling the activity of photosystem (protein complexes involved in photosynthesis) PS II and I (Z-scheme; the light-dependent reaction, which converts solar energy into chemical energy). In anaerobic conditions, they are also able to use only PS I - cyclic photophosphorylation - with electron donors other than water (hydrogen sulfide, thiosulphate, or even molecular hydrogen) just like purple photosynthetic bacteria. Cyanobacteria also have the ability to reduce elemental sulfur by anaerobic respiration in the dark. A unique aspect of these organisms is that their photosynthetic electron transport shares the same compartment as the components of respiratory electron transport. It is the thylakoid membrane (the site of the light-dependent reactions of photosynthesis) hosts both respiratory and photosynthetic electron transport, while the plasma membrane contains only components of the respiratory chain.

TREATMENT (eradication)

With some of the above information in hand, one can now make more informed choices about how to eradicate Cyanobacteria.

*30% water change (or more) using a Gravel Vacuum (especially to remove nitrogenous waste producing mulm than often accumulates under rocks or UGF plates). This cuts off one source of nutrition. Removing hydrogen sulfate producing anaerobic bacteria in freshwater is important as well, so make sure and vacuum all the dead spots. Along this line of thought, removing sand and replacing with gravel has helped in aquariums I have monitored with BG algae

*Electrolytes and minor elements such as magnesium and calcium, Wonder Shells are useful here. VERY IMPORTANT.

*Add a UV Sterilizer (Very effective but not always cost effective for small aquariums, but is worth mentioning, not just for sterilization, but for Redox which plays a role in controlling bacterial BG algae.)

*Improve the Redox Potential, this is often missed, however this is an important part of the equation. For more, please read this article: THE REDOX POTENTIAL IN AQUARIUMS (& PONDS); and how it relates to proper aquatic health

*Cut back on feeding and improve food quality (No TetraMin). Better choices: Ocean Nutrition, HBH, Spirulina 20 just to name a few. This again will cut back on nutrients.

*Increase circulation and dissolved oxygen. These Prokaryote Bacteria do not do as well in a well oxygenated/ circulated environment (remember my points about the lakes).

*Medication; Copper at a level of 15 to 20 ppm is effective in inhibiting effective photosynthesis. Erythromycin has shown to be effective here as well.

*Lighting; although this is often recommended for the eradication of Cynabacteria, this is often not effective and the BG algae bounces right back. The reason is as stated above that Cyanobacteria have the ability to reduce elemental sulfur by anaerobic respiration in the dark.

For my full and expanding article, please follow this link: Blue Green Algae (Cyanobacteria) in Aquariums; what it is and how to control it.