Aquarium Algae Identifier – Green Water, Hair, BBA & More

Green water is caused by a sudden bloom of free-floating single-celled algae (phytoplankton). The most common triggers are excess light (especially direct sunlight), elevated ammonia or nitrate levels, and insufficient filtration. A UV sterilizer is the fastest solution—it kills the algae as water passes through. Also reduce your photoperiod to 6-8 hours and perform partial water changes to lower nutrient levels.

BBA (Audouinella sp.) appears as dark gray to black dense tufts, often on leaf edges, driftwood, and hardscape. It thrives in environments with unstable CO₂ levels, strong water flow, and excess dissolved organics. The most effective treatment is spot-dosing liquid carbon (glutaraldehyde-based products like Seachem Excel) directly onto affected areas using a syringe. Stabilize your CO₂ injection, reduce flow, and manually remove heavily affected leaves. Siamese Algae Eaters (SAE) and Amano shrimp may also help control mild cases.

Hair Algae is bright to dark green, soft, and forms long flowing strands that easily wrap around plants. It feels slippery and pulls apart easily. Staghorn Algae is grayish-green with a distinctive branching pattern resembling deer antlers. It's coarser and more brittle—when pulled, it tends to snap rather than stretch. Hair algae often indicates iron excess or CO₂ deficiency, while staghorn algae typically points to ammonia spikes or poor filtration.

No—despite its name, Blue-Green Algae (BGA) is actually cyanobacteria, a photosynthetic bacteria. It forms slimy, sheet-like patches that are usually blue-green but can also be reddish or black. It has a distinct earthy/musty smell. BGA often appears in areas with low nitrates, poor water circulation, and decaying organic matter in the substrate. Treatment includes improving flow, vacuuming the substrate, raising nitrate levels slightly, and in severe cases, using erythromycin (with extreme caution as it affects beneficial bacteria).

Brown algae (diatoms) are extremely common in newly established aquariums (first 2-6 weeks). They feed on silicates leaching from new substrate, glass, and silicone seals. They also thrive in low-light conditions. The good news: diatoms usually disappear on their own as the tank matures and silicates are depleted. Otocinclus catfish, Nerite snails, and Amano shrimp are excellent diatom consumers. Increasing light intensity and duration can also help since diatoms prefer lower light while green algae outcompetes them in brighter conditions.

Green Spot Algae (GSA) forms hard, circular green dots on glass and slow-growing plant leaves. It's strongly associated with phosphate deficiency (PO₄ below 0.1 ppm) combined with high light intensity. Unlike most algae problems that benefit from nutrient reduction, GSA actually requires increasing phosphate levels to around 0.5-1.0 ppm. Manual removal from glass requires a razor blade or abrasive pad—magnetic cleaners usually can't remove it. Nerite snails are one of the few creatures that effectively consume GSA.

Not necessarily! A small amount of algae is natural and healthy—it indicates a functioning ecosystem. Algae produces oxygen, consumes excess nutrients, and serves as food for many aquarium inhabitants. Many advanced aquascapers intentionally cultivate certain algae types (like green spot algae on hardscape) for a natural look. Algae only becomes a problem when it grows out of control, indicating an underlying imbalance in light, CO₂, or nutrients. Think of algae as a symptom, not the disease itself—treating the root cause is always more effective than just removing the algae.