Green Sea Hare question

I had mine in the tank for about a year and a half until I had to breakdown the tank... IME it is normal for them to eat and then burrow into the sand they can spend half a day like that and then come out once more to eat... Mine eat my hair algae in the tank and then I started giving him nori sheets and he seemed to thrive, I had to give him back to the LFS when I broke down my tank to move.. if you keep good water parameters and the intake and power heads covered he will be fine