Something I found on the web real quick
As the cycling process nears an end, many hobbyists notice an improvement in the appetite and overall deportment of their fish. In addition, a small green algae bloom will often accompany the drop in nitrites and rise of nitrates. The cycle is over and the tank ready for additional fish when both the ammonia and nitrite are zero and the nitrate has begun to rise. This is an appropriate time for a first routine partial water change.