24 tents around the mouths mean it is Goniopora for sure. I feed mine a mixture of cyclop-eeze, live phyto, and dt's oyster eggs. You can probably get away with using concentrated phyto as well. It may take a little while before you actually notice it actually eat, but word has it that the food only has to touch the mouth for them to gain some nutrition. One of mine, which has smaller polyps than yours, develops a thick mucous slime when I target feed it which holds the food in since most of it is too large for it to digest.
They like medium-low light, and medium-low flow. They should have a gentle current, but not so much that they look like they're going to be torn off their skeleton.
The reason for taking it off the sand is because most of the species of Goniopora aren't free-living specimens. If you look on the bottom of it or somewhere else, and see an area where it's been broken/chiseled off a larger colony then you have one that doesn't belong in the sand.
They are considered to be hard to care for corals but only because they have special care requirements. The two main reaons why they die in captivity is from starvation and brown jelly disease. Taking it out of the sand *gently* should keep it from getting brown jelly disease. Be very careful when you handle the coral also because if you damage the tissue, it can also develop brown jelly disease. If it's going to get brown jelly, it will usually start around the perimeter of the coral where it's been in the sand, and in early cases you may not even be able to see the brown jelly but if you notice any tissue falling off or receding tissue then keep a close eye on it and you may want to give it an iodine dip for a couple days.
If you take really good care of it, you should start to see better polyp extension in the next couple of months and it'll probably colour up a bit more too.