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Symptoms, common causes and what to check — for the most common aquarium issues.
Diagnose my problemWater quality slowly worsens over months or years despite regular small water changes.
Milky or hazy water that never fully clears.
Slimy blue-green or dark purple patches with a foul odor.
Elevated ammonia levels cause burns, redness and rapid breathing.
Long green strands coat plants, hardscape and glass. Common in young or bright tanks.
Grey-green branching tufts shaped like antlers on plant tips and filter outlets.
Dark, hairy tufts that cling to hardscape and slow-growing plants.
A dusty brown coating on glass, plants and decor, common in new tanks.
Water turns bright green from suspended single-celled algae.
Fins look frayed, ragged or are visibly shrinking with white or red edges.
Abdomen swells and scales stand out like a pinecone — usually a bacterial infection.
Sudden temperature swings after water changes, heater failure or power cuts stress fish.
Fish hover at the surface, breathing rapidly. A possible oxygen emergency.
Fish hide constantly, refuse food and fade in color.
Tiny white salt-like grains on the body and fins of fish.