[Delphinus]

IME/IMO nonphotosynthetic gorgs are far more difficult to keep alive than photosynthetic ones. Most of the time they wither and eventually disappear.

Generally speaking feeding them just once or twice a day is not sufficient for long-term success because they really need to feed continuously. The most successful setups I have seen that did well with these involved a drip type autofeeder that is on 24/7. If you're really into gearing out then it can be a fun project but if what you're after is an easy coral you don't need to worry about then what you really want to focus on are the photosynthetic gorgs. Light and flow and a good solid base (glue them to a heavy rock) and really they'll just take care of the rest.

The other problem with feeding the non-PS ones is nutrient control/management.

The best way to tell the two apart is the colour of the polyps. Zooxanthellae is typically brown; so if the polyps are brown the coral is very likely photosynthetic. Brightly coloured polyps, or pure white polyps, are those without zooxanthellae will require feeding and what they feed on will vary from species to species (and is generally related to the size of food they're after).