This can happen, it sounds like you're still cycling (and the serpaes are stressed). I would really recommend some SafeStart for this purpose, 5ppm nitrites is very dangerous.For a week and a half after adding my Serpaes i battled Ammonia, Nitrite and Nitrate levels. My Ammonia and Nitrite would spike and then Nitrates. I did water changes nearly daily. then the Nitrites stabilized at 0 for about a week and Ammonia was very low but i continued to do Watet changes. Then when the Ammonia hit 0 and stayed i still ended up doing water changes because my Nitrate was high around 40ppm and i was also doing water changes because the water was turning brownish green and very dirty. After water changes it looked much cleaner. Yesterday was about the first day i did no water change.
I have also noticed when Nitrites spike, the Serpaes become highly aggressive to each other.