Welcome!
Ok let me ask some questions so we can get a better feel of your situation.

What kind of tadpoles? Where did you source them from?
How big is the tank? How long has it been set up?
Temperature?
What type of filtration? Do you know your readings for ammonia, nitrite, and nitrate?
How often and how much water do you change? What type of treatment do you add to the water?

Don't worry - we will help get you sorted out!

Pictures are also helpful