How to change aquarium water effectively and safely?

To change aquarium water effectively and safely, follow these steps:

1. Use a siphon to remove about 25-30 of the water from the tank.
2. Clean the gravel and decorations with a gravel vacuum.
3. Use a water conditioner to treat the new water before adding it to the tank.
4. Slowly add the treated water back into the tank to avoid stressing the fish.
5. Monitor the water parameters regularly to ensure a healthy environment for your fish.