That's a good sign that your cycling is going well. The bacteria that consume the ammonia are now established, that's why your ammonia is 0. From now on, any ammonia from the turtle's waste will be converted directly to nitrite. So you shouldn't see anymore ammonia from your test kit as long as the bacteria culture stays healthy.
Now you have to wait for the next type of bacteria to grow and consume the nitrite, then you will see the nitrite levels go down to 0. The final product is nitrate which accumulates slower and is tolerated by the turtles much better (but it will add to the algae growth).
Don't worry, it sounds like everything is going well. Relax and enjoy!
