Cyanobacteria
Cyanobacteria, commonly shortened to cyano in the hobby, is a type of photosynthetic bacteria, not a true algae, that forms distinctive slimy mats in shades of red, maroon, green, or occasionally black across rock, sand, and other surfaces. Unlike hair algae, cyano typically appears as a smooth, film-like sheet that can be lifted off in one piece and often produces small bubbles from trapped oxygen during active photosynthesis.
Its presence usually points to an underlying imbalance, most commonly elevated nutrients, poor flow, or low oxygen in specific areas, making outbreaks a useful diagnostic signal as much as a cosmetic nuisance.
Why It’s Important
- Signals underlying nutrient imbalances or poor flow that may need broader attention.
- Can spread rapidly across rock and sand once established, quickly becoming visually significant.
- Sometimes produces compounds that can be irritating to sensitive corals or other livestock nearby.
- Often persists until its root cause, rather than just the visible bacteria itself, is addressed.
How It Works
Cyanobacteria thrives in conditions with elevated nutrients, particularly phosphate and nitrate, combined with stagnant flow and adequate light. It forms mats by growing across a surface in interconnected colonies, often trapping small gas bubbles produced during photosynthesis that give the mat a slightly bubbly texture.
Because these mats can regrow quickly from even small remaining patches, physical removal alone rarely provides a lasting solution unless it’s paired with improvements to flow and a reduction in the nutrients fueling the outbreak in the first place.
Cyanobacteria and Related Parameters
Cyanobacteria outbreaks are closely tied to nitrate and phosphate levels, the nutrients most commonly driving growth, and to flow rate and dead spots, areas of poor circulation where outbreaks often start. It’s also relevant to nutrient export methods like protein skimming and carbon dosing, commonly used to address the underlying cause.
Addressing a cyanobacteria outbreak typically involves a multi-pronged approach: improving flow to eliminate stagnant areas, reducing nutrient inputs through more careful feeding or better nutrient export, and physically removing existing mats through siphoning during water changes. Some reef keepers also use UV sterilizers or specific anti-cyanobacteria treatments for particularly stubborn outbreaks, though addressing root causes generally produces more lasting results.
Cyanobacteria outbreaks are also relatively common during a tank’s early months, since new systems often carry elevated nutrients and less established competition from other organisms. In these cases, outbreaks frequently resolve on their own as the tank matures and its nutrient export capacity catches up, though persistent or worsening outbreaks in an established system usually point to a more specific underlying issue worth investigating directly.
Common Misconception
A common misconception is that cyanobacteria is simply another form of algae and should be treated the same way. Because it’s actually a photosynthetic bacteria with different growth patterns and vulnerabilities, algae-focused treatments don’t always work well, and addressing flow and nutrient export tends to be more effective than typical algae control methods.
The Bottom Line
Cyanobacteria is a photosynthetic bacteria that forms slimy mats when nutrients are elevated and flow is poor, serving as a useful diagnostic signal in a reef tank. Addressing its underlying causes, rather than just removing visible mats, is key to preventing it from returning.
