I NEED HELP!

Question
I started my first fish tank and everything was going really good until the water level went down to low and I had to add water.  I added tap water to it and by that night almost all of my fish died.  What did I do wrong?  Also the water has a smell to it like it's old stagnant water but I have a double filter running that I just bought.  What could cause it to smell?

Answer
Stacey,

 When you added the new water did you condition it to remove the chlorine? Some people do not know that they have to remove chlorine from their water before adding it to the tank. Also, the water coming into the tank has to be the same temp as the water already there. When the water is too cold or too warm the fish can go into shock and die. You can get a water conditioner from your local fish store. Follow the directions on the bottle and use it every time you add water.