I would ignore nitrite reading of 0.4 or 0.5 as test kit noise. If livestock k is doing fine I would ignore it. By the way ammonia upto 0.2 ppm NH3 is also not going to hurt the fish either. I think you should just do a 25% water change and just enjoy the tank.
You have fish and corals in the tank and thus ammonia and nitrite can fluctuate from hour to hour days to day.
You have fish and corals in the tank and thus ammonia and nitrite can fluctuate from hour to hour days to day.