IMHO it depends a little on what your RFA looks like. I collect them in the Florida Keys and have about 30 of them in my 40g tank at the moment. There are 2 breeding adults, about 5 or 6 very near adults, a handful of young ones (6 to 12 months old) and about 10 to 15 brand new babies.
I've found that the more colorful and highly fluorescent RFA's come from deeper water and are less able to do enough photosynthesis to do well without some additional feeding. But they will eat almost anything you offer them. I feed a wide mix of different foods and once every week or two I shutdown the flow and feed them directly with a turkey baster. Than about 10 to 15 minutes later I start the pumps back up. If you want them to breed, they need to be fed regularly (almost weekly).
The less colorful RFA's come from shallower water and are much better at doing photosynthesis because they have more zooxanthellae inside. These seem to grow and do just fine without any special attention.
Now this doesn't mean that the colorful RFA's will suffer if not fed. If you feed the tank (fish and coral) well, the RFA's may do OK. But if you see them getting smaller in size over time, say 2 or 3 months, you should probably consider direct feeding. RFA's can get smaller and bigger in short cycles of a few days to a week. Like most anemones, they are mostly water and can change size easily.
There is a link in my signature below to an informative discussion about RFA's and there needs. Please join in, ask questions.
