Aquarium Fish Care: A Practical Guide
Fish are easy to keep badly and rewarding to keep well. Two ideas — the nitrogen cycle and quarantine — separate the two.
The Nitrogen Cycle (New Tank Syndrome)
A brand-new tank has no beneficial bacteria to process waste. Within the first ~6 weeks, total ammonia nitrogen and nitrite can spike and poison the fish, producing lethargy, anorexia, and sudden death — the classic "new tank syndrome." Cycle the tank first (fishless cycling with an ammonia source, monitoring until ammonia and nitrite read zero) or stock slowly with frequent water changes. It can take up to 8 weeks for a biofilter to establish.
Quarantine
Quarantine new fish for at least 30 days in a separate system with its own equipment; many infections arrive on apparently healthy fish and tear through an established tank.
Water Quality
Fish are poikilothermic, so temperature drives their metabolism; match species needs and avoid swings. Dissolved oxygen, pH, and salinity (for marines) all matter, and low oxygen or other water-quality problems predispose to hemorrhagic septicemia and parasites.
Health Watch
- Gill disease and parasites — common, often stress-driven; good water quality is the best prevention.
- Medication resistance — routine prophylactic medication selects for resistant pathogens; treat specifically, not preventively.
- Legality — some fish and many aquatic plants are restricted under wildlife laws (e.g., the US Lacey Act), so confirm before importing or releasing.
Stable, cycled, quarantined water does most of the work; everything else is detail.