All aquariums have some algae - the goal is balance, not zero. Common types: 1) Brown diatoms (silica-fed, common in tanks under 4 months, otocinclus + nerite snails clear it). 2) Green spot (high-light, low CO2 - normal on glass + slow plants). 3) Green water (single-cell algae bloom, UV sterilizer or 3-day blackout). 4) Hair / thread algae (high-light + low-CO2 imbalance, manual removal + amano shrimp). 5) Black beard (BBA - low CO2, high organics; spot-treat with Excel/Easy-Carbo). 6) Cyanobacteria red slime (low flow + high organics + low nitrate; ChemiClean or Maracyn). Root causes: too long photoperiod (cap at 8h), direct sunlight (move tank or curtain), overfeeding (more food = more nutrients = more algae), uncycled tank, no plants competing for nutrients, dirty filter, low flow areas. Algae crew: nerite snails (everywhere), amano shrimp (hair algae specialists), otocinclus (diatoms + soft green), bristlenose plecos (community FW, 30g+), cherry shrimp (biofilm + leftover food). Saltwater: tangs, foxface, urchins, turbo snails, trochus. Nuclear option: 3-day blackout (cover tank, lights off, fish ok) clears most algae blooms.
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