Fin rot is a bacterial infection (typically Aeromonas, Pseudomonas, or Vibrio) that causes ragged, eroded, or discolored fins. Common opportunistic infection triggered by poor water quality or wounds.
Poor water quality (high ammonia/nitrite/nitrate), aggressive tankmate damage, fin nipping, or rough handling during shipping.
Multiple effective treatments exist. Pick based on your tank type, livestock sensitivity, and severity. Always treat in a separate quarantine/hospital tank - most medications are toxic to coral, invertebrates, and live rock biology.
Maintain perfect water (0 ammonia, 0 nitrite, <20 nitrate). Remove aggressive tankmates. Avoid fin-nippers like tiger barbs in community tanks.
Ragged or torn fin edges. White or black edges on fins. Fins shortening over days.
Poor water quality (high ammonia/nitrite/nitrate), aggressive tankmate damage, fin nipping, or rough handling during shipping.
Water change + clean conditions: For mild cases: 50% water change, perfect water parameters, no further treatment needed. Fins regrow in 2-4 weeks.
Maintain perfect water (0 ammonia, 0 nitrite, <20 nitrate). Remove aggressive tankmates. Avoid fin-nippers like tiger barbs in community tanks.
Mild to moderate - usually treatable
Always treat in a separate quarantine or hospital tank. Most medications are toxic to coral, invertebrates, and live rock biology.
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.
Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.
Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.
Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.
Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.
Species-appropriate husbandry: research adult size, territoriality, diet, and tankmate compatibility before purchase. Use our tank stocking calculator + compatibility guides.
How long does an aquarium take to set up? 4-6 weeks for full cycling + first stocking. Use our cycle ETA calculator + how long does cycling take.
What's the best aquarium for beginners? 20-gallon long. Big enough for parameter stability, small enough for budget + space. See beginner picks.
How often should I do water changes? 25-30% weekly. See water change frequency Q&A + water change calculator.
Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.
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