There's a lot of controversy about keeping Linkias. The common wisdom seems to be that we can only speculate about what, specifically, it is that they eat. Some say that becuase of that, it's unlikely that anyone would be successful keeping then over the long term. I have three and have had the orange one the longest of the three...well over a year. The purple one's been a good long time, too. The blue one is in my reef for about four months or so. The orange one has grown significantly and had gotten one of its "arms" caught in a power head so I had to cut more about an inch off of it with a razor blade...It's fully grown back now. So, I say this because I believe that it's a clear sign that they are being nourished. I can't say specifically what it is that they do eat because I never see them take a particular food that I put in the tank. But, I think that if you have a lot of live rock in your reef and the tank is well aged....say, at least two years...it should get what it needs.