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ProblemsTemperature Shock

fish

Temperature Shock

Sudden temperature swings after water changes, heater failure or power cuts stress fish.

Symptoms

Fish darting or flashing after a water change
Sudden listlessness or gasping
Clamped fins and rapid breathing

Common Causes

Adding water of a very different temperature
Heater failure or stuck thermostat
Power outage in cold months

What to Check

Water temperature before and after changes
Heater function and wattage vs tank size
Thermometer accuracy

What Not to Do

Do not pour warm water straight into the tank
Do not raise temperature more than 1–2 °C per day during treatment

Recommended

How to Change Aquarium Water Without Stressing Fish Setting Up a 40cm Aquarium for Beginners: Step by Step Tool: Water Change Calculator

This guide is informational and does not replace professional veterinary advice. If fish are severely ill, consult a veterinarian.