Just a few suggestions, I know you said the light is new, but maybe the long tenicle doesn't like that particular light. Is that the same one you got from me last year, if so, he should be a beautiful blue/green color, almost a teal. He likes light, just not directly over it. He does eat silversides. He was not real aggressive, but did not like being messed with. and definately doesn't like an other anemone by it. Either way anemones have a habit of going where they want. You can try over and over to put him where you think he should be, but if he doesn't like it, he will move somewhere he feels better. If he keeps going under the rocks, I would take it as he is stressed, and not feeling very well.
If you keep moving your rocks around, that could be stressing them also.
For now I would try to get the tube anemone away from the long tenicle. Stop moving the rocks around, maybe the long tenicle can calm down. And start offering him a silverside. It may not take it whole so chop it up into a few chuncks.
The main thing your need to understand is the more you mess with your tank, the more upset the residents will be.