No, you should not put tap water directly into a tank with little fish.
* Chlorine and chloramine: Toxic to fish; added to tap water to kill bacteria.
* Other chemicals: Heavy metals, pesticides, or high mineral concentrations may be present.
* pH and hardness: Tap water often differs from what fish need; sudden changes can stress or harm them.
What to do instead:
1. Condition the water: Use an aquarium water conditioner to remove chlorine, chloramine, and other harmful substances.
2. Let tap water sit: Allow it to sit in an open container for 24 hours to let chlorine dissipate (less effective than conditioner).
3. Use dechlorinated water: Some pet stores sell pre-treated water.
4. Test your water: Check pH, ammonia, nitrite, nitrate, and hardness before adding fish.
Important note: Always follow the instructions on your water conditioner product.