This unsightly and potentially hazardous primitive life-form is the bane of many an aquarist. The colour is the least identification for this life-form, the most common is the blue-green colour i.e. the cyan; then it can be red, brown, black, you name it all of them slimy and spreading to cover entire surfaces, choking to death other plants and algae and causing fluctuations of water ph and causing stress to the aquatic life around them. Kill it and a dying cyno-bacter bloom will release toxins into the water and while decaying absorb nearly all the oxygen in the water body suffocating the aerobic life-forms present.
Please don’t hate or curse this unwanted life-form; it may be to this primitive life form with prokaryotic (lacking cell membrane) cells and ability to photosynthesize their food from the minerals and CO2 present in water ( that is their metabolic system) the rest of the life-forms you see around you(and you yourself) owe their existence! The Cyanobacteria is so primitive as to have been the life form which created the oxygen contained in the atmosphere on primitive earth. Which enabled all the life system we see today to breathe life giving oxygen?
The group of life-forms we call ‘Cyanobacteria’ have evolved many adaptations to their environment. Some can use longer wavelengths of light and colonize deeper water, some can absorb UV, and some can survive long spells of darkness, and as you would expect there are freshwater, brackish and marine adaptations too. Cyanobacteria use air filled vacuoles to regulate their depth of colonization. No wonder then that most aquarist have trouble eradicating this life-form from their aquariums.
More primitive a life-form is, less are the parameters required to find a suitable niche to adapt to. So the niches available to the Cyanobacteria to colonize are greater than for algae, and it is because of this that an aquarist may avoid algae but still have a Cyanobacteria attack. Then how do you avoid the Cyanobacteria? Some will tell you that a good circulation in the aquarium will do it. Perhaps and perhaps not. A good circulation would reduce stratification in the aquarium and thus reduce the number of niches available. Less number of niches is not an avoidance of a niche suitable for the Cyanobacteria, but a chance that there are none. So yes reduce the number of niches and hope that you don’t have a Cyanobacteria attack.
What then is the surest way to avoid a Cyanobacteria attack? Very easy to answer that; “deny it what it needs”.
What do the Cyanobacteria need? Water, nutrients, CO2, and light. The first three cannot be denied by an aquarist, although he may be able to reduce the nutrients by regular water changes and the CO2 by using an aerator, which would not allow a CO2 richer water that an open water body. So what it boils down to is light management.
Will light management alone stop all chances of Cyanobacteria growth? The answer is an emphatic “NO”. It is only with all the tools can you keep the Cyanobacteria bloom at bay, but some Cyanobacteria will always be present, just like algae you cannot have an aquarium entirely free from Cyanobacteria or Algae but you can restrict both of them overtaking your tanks.
Keep a good circulation in the tank to reduce the niches, keep the available nutrients low, control the CO2 in non-planted aquarium, keep the light period short in non-planted aquariums and the light intensity low, in planted aquarium regulate your light to your plant cover and growth, and then pray that you don’t have a Cyanobacteria bloom.
If your prayers are not answered, act fast. If you find the Cyanobacteria has formed a spreading (increasing in size) patch, just remove it along with whatever it was growing on and treat it with hydrogen peroxide or erythromycin to kill it. After treatment, a good rinse and you can put it back.