We don't worry much about nitrate so just regular water changes to keep it in check. Ammonia and nitrite, however, need to be 0. Even a slight elevation will cause stress or death. If you are experiencing a bit of nitrate, it sounds like your tank is well cycled and THAT is a good thing
This definitely looks like a medium to large species and most will be visible during the day. Keep in mind that they do not fully acclimate for about a month and we usually see quite a behavior change after that adjustment. Sometimes they become more active and interactive and sometimes the opposite. Anecdotally it seems to depend upon the individual animal more than on the species or environment.
I think I am jealous, beautiful animal!