Here's why:
* Chemicals: Cleaning products, even if "fish-safe," can still be harmful in concentrated amounts.
* Water quality: Cleaning disrupts the water chemistry and can cause spikes in ammonia and nitrates, which are toxic to fish.
* Stress: Cleaning can be stressful for fish, and being in a dirty tank while cleaning can make it worse.
Here's what you should do:
1. Prepare a safe temporary container: This could be a bucket, a separate aquarium, or even a large plastic tub. Make sure the water is dechlorinated and at the same temperature as your main tank.
2. Gently net your fish: Use a net that's large enough to avoid injuring them. Be careful not to scare them.
3. Clean your tank thoroughly: Follow your usual cleaning routine.
4. Return the fish to their clean tank: Make sure the water is the same temperature before you add them back.
Never leave fish in the tank while cleaning!