Hypoxia

Definition

Hypoxia in aquariums is insufficient dissolved oxygen (DO) - fish can't extract enough oxygen from water. Caused by overstocking, dirty filter, low surface agitation, or warm water (warm water holds less O2).

Practical use

Symptoms: fish gasping at surface, rapid gill movement, sudden mass die-off. Fix: add powerhead/airstone for surface agitation, reduce stocking, cool tank below 82°F.

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