Hi there,
amonia turns into nitrite and nitrite turns into nitrate. Your tanks seams to be cycling.
I would do a 10/20 % water change to get your nitrite down.
In your other tank, the tank hasn't cycled at all. you will need to do a water change. I've bought from pets at home a bottle of stuff called "cycle" which removes amonia and nitrite from the water. real plants can reduce nitrate.
Hope this helps,
Martyn