What is the lighting on an eclipse? just flourescents? if so find the closest thing you can to a 10k type bulb, like an aquasun or something, and try mushroom corals, I would normally attempt an elephant ear type mushroom, but in a 12 gallon that might be a bit much, maybe just get a couple of frilled mushrooms, or hairy mushrooms. Be sure to try and find a nice rock of them, or atleast a good sized one because you will not get much if any growth out of it.
Mushrooms are hardy as heck, and can live with minimal lighting, while nobody is going to out right promise that mushrooms will make it in that lighting, I have seen it.
<story reading is optional>
A local guy set up a fish only tank and when he did he wanted some rocks in there, rather then rresearch it all out, he went online and ordered 50# of live rock from some ebay store.
I told him I would never let him live down that fact that by the time all was paid for he spent like $7 bucks a pound any ways.
Well when he got the live rock I had my foot in my mouth, it was probablly 40% covered in coralline, one large rock had about 4 mushroom starts on it, one rock had a pistol shrimp hideing in it, and another had some nice macro and a pretty greenish blue sponge on it.
Anyways he put it all in his fish only tank with flourescents, and the macro, the sponge and the mushrooms did ok, the sponge and the mush rooms grew so slow you would not notice any growth unless you hadn't looked at his tank for a month.
So they can live that way, just not well.
Much better than when they were hosting our Sinularia (spaghetti leather), they were loving that one to death so we moved it to the other side of the tank.
