NO2 is converted into NO3 by denitryfying bacteria. The more NO2 u have, the more it is converted into NO3, and thus u have alot of NO3. It works like this. So if u have alot of ammonia, all will be converted to nitrite. then u will have no ammonia, and alot of nitrite. when all ur nitrite is converted to nitrate, u will have no nitrite and alot of nitrate. it works like this. all 3 are connected. A spike in ammonia or nitrite will give u a spike in nitrate, and a decrease in ammonia/nitrite.