Most fish do not need to be removed during a routine water change. Switch off equipment that must not run dry, siphon the planned amount while avoiding the fish, condition tap water for chlorine or chloramine, match the replacement temperature and refill slowly. Keep hands and tools moving calmly, avoid dismantling the aquascape unnecessarily and restart equipment as soon as the water level is safe.
A water change should feel like routine maintenance, not a tank evacuation. Catching every fish usually creates far more stress than leaving them in familiar surroundings while you work around them.
Prepare everything before you start
- Bucket or hose used only for aquarium work.
- Water conditioner.
- Thermometer.
- Gravel vacuum if substrate cleaning is planned.
- Towels for spills.
- Any pre-mixed RO or remineralised water needed for the tank.
Leave the fish in the aquarium
For ordinary partial changes, there is no need to net the fish. Move the siphon slowly and keep an eye on small fish, shrimp and fry near the intake.
If necessary, cover the siphon opening with a suitable guard in tanks containing very small animals.
Avoid temperature and chemistry shock
Measure replacement-water temperature instead of judging by hand. Treat chlorine or chloramine before the new water contacts fish or biological media.
If your tank uses modified GH, KH or RO water, prepare the replacement mix consistently.
Refill gently
Pour onto a plate, bag or hardscape if direct flow would churn the substrate. With hose systems, control the flow so fish are not pinned by a sudden jet.
A slow refill is especially useful with delicate plants, shrimp and small fish.
Restart and verify equipment
Make sure heaters and filters are back on, filters have primed correctly and the water level is normal. Check for leaks and observe fish for several minutes before walking away.
Related aquarium tools and guides
Frequently asked questions
Should I remove fish during a water change?
Usually no. Leaving them in the tank is less stressful for routine partial changes.
Why do my fish hide after a water change?
Brief hiding can follow disturbance, but check temperature, conditioner dosing and water chemistry if behaviour looks severe or prolonged.
Should I feed fish before a water change?
There is usually no need. Feeding immediately beforehand can add waste during maintenance.
Sources and further reading
This guide separates general aquarium arithmetic from fish-welfare decisions. For species-specific limits, always check the needs of the fish you intend to keep.