Well, the water isn't right at the end.
Think about it -
The bacteria have changed all the ammonia to nitrite - good
The bacteria have changed all the nitrite to nitrate - good
The nitrate is now really high - bad!!!
At the end of the cycle the nitrate levels will be about 80 or so, whereas you should never allow the to get above 30-40 maximum, and mostly it will be about 10-20 when the tank is up and running and you are doing weekly water changes.
So, you do your 80% weater change, get that number way down, and then keep it down by good weekly tank maintainence - water changes and gravel vac's