Help with Dragon Wrasse!

I have had a dragon wrasse for over a year and a half and it is the most hardiest fish I have had. But anytime I do anything in the tank I wont see him for days. I bought another dragon wrasse about a month ago and it has been good. But the other day I added an eel and my new dragon wrasse has been lying in the live rock (about a 2" hole in the rock that leads to the sand) So he is just lying on top of the sand inside the rock. I can see him and see that he is alive, he changes position but has been lying there for 2 days now. I wonder if my sand is too heavy for him to burry himself? most of the sand is crushed coral. The fish is 1 1/2 - 2 inchs long. I have a 220 gallon tank, ammonia-0, nitrate-0, nitrite-0, ph-8.2, salinity-1.028. The other thing is I started having green hair algae, and I saw him swimming though it over and over again. ANY IDEAS!