Help

[Kado]

My Neo Tret is about 1.2 inches long and has been in the tank since day 1 with my other cichlids and has coped well and been very active. For 48 hours now he has put himself in this small hole in the rocks and stays there motionless for most of the time only moves when I feed them or to chase another fish off if they get too close and then returns immediately.
I've tested the water temp. Ph, ammonia and I did a 20% water change 4 days ago. Everything else seems fine. Can anyone shed some light please