There's an ammonia cycle which everyone is familiar with and when that's done its ok to add livestock. However, the tank undergoes maturity which in itself is a different cycle of it's own. This is what the others are referring to. The tank although can process ammonia still is in the process of seeding other necessary bacteria as well as stabilizing parameters. You will see blooms and even algae outbreaks throughout this process. Also parameters swings as well. This is normal and even with the best husbandry may still occur. Just be patient and you will see as your tank matures, the better it will handle itself and grow corals. Also, hope you mean your nitrate is 5 and not your nitrite because that means you haven't finished a cycle.