Mature tank! HIGH FLOW! LOW LIGHT, unless it a photosynthetic one. fThey tend to do best in LPS tanks as these tend to be a bit dirtier, and there are more nutrients suspended in the water column. Feeding of small enough sized fodd particles when the feeding tentacles are out is also essential. Soem gorgos are quite a bit hardier than others, adn the photosynthetic ones are also typically easier to care for, as all the really need is light. Deep Sea yellow adn red gorgos are probably the easiest of the non photosynthetic ones to keep, Blueberries are quite difficult, adn almost always perish in just a few months. Quite a bunch of people have posted that placement directly in the flow of a ph is their secret to success. My yellow and orange spiny are doing great, but I did lose a blueberry unfortunately. Check these forums for more info, and SWF.com offers some that are great candidates.
Hope this helps.