What type of cyno is he? I had an eypterus for 28 years (my dad got him 3 years before i was born) very hardy fish and intelligent. As far as i can tell from the pic he will outgrow his lair in a few years you might consider getting him a larger cave for a future moving.
The green terrors grow up to a max of 30cm(usually though they stop around 20) When they reach maturity they became quite the aggressors. They like to dig and guite usually they might even up-route plants (especially when grown).
Dont worry that he doesnt eat them yet. Those fish eat a wide variety of foods but sometimes it takes some using into them.