As stated, if no ammonia or nitrite present and you are reading some nitrate, the cycle is complete. However, there is a bioload tolerance, to speak of. This means that you can overstock the tank to where the bacteria cannot handle the livestock added thus creating a nutrient overload and again show nitrite. Ammonia levels can also rise causing death. I would suggest a cleaup crew after a water change. You do want some nitrate but not too much. You do not want to have too clean of a tank either because phosphates and nitrates are needed by bacteria, fish and corals.(All tanks will have cycles especially during the first 6 months or so due to adding livestock.) The cleanup crew can help with any algae and/or cyano that shows up. Again, after the tank is cycled, there are still things happening in the tank which means your tank is not mature/still undergoing changes for many months to come. HTH.