Cyanobacteria (cyano) appear as red, brown, or black slime sheets that coat substrate, rocks, and equipment. Not technically algae - it is a photosynthetic bacterium. Releases trapped phosphates when disturbed, fueling further blooms.
Excess phosphate (>0.1 ppm) combined with low flow + new tank or post-cycle nutrient imbalance.
Always treat in a separate quarantine tank.
Maintain phosphate <0.05 ppm + nitrate 5-10 ppm. Avoid stagnant low-flow zones. Don't overfeed.
Red, brown, or dark green slime sheets. Bubbles forming under the slime. Sudden appearance after a parameter change.
Excess phosphate (>0.1 ppm) combined with low flow + new tank or post-cycle nutrient imbalance.
Increase flow: Add a powerhead or angle existing flow to disrupt the affected area. Cyano cannot grow in high-turbulence zones.
Maintain phosphate <0.05 ppm + nitrate 5-10 ppm. Avoid stagnant low-flow zones. Don't overfeed.
Mild but persistent if untreated
Browse the full disease database for 45 aquarium conditions with treatment protocols, or check the care library for prevention-focused husbandry guides. Use our symptom matcher to rank likely diseases from observed signs, the water parameter checker to diagnose related water-quality issues, or the QT timeline calculator to plan a treatment schedule.