What sort of Goniopora do you have? The different species in the genus have a pretty wide variety of sizes. I found a pretty good article on the subject. http://www.advancedaquarist.com/2005/10/aafeature2
I have a specimen of Goniopora pandoraensis (or a similar species) in my tank. I haven't been feeding it, but after reading that article I think I will try oyster eggs or cyclop-eeze. Interestingly, the photo of Goniopora pandoraensis in the article is a specimen with degenerate tentacles. There is an older article by Julian Sprung on Advanced Aquarist regarding goniopora in which he comes to the conclusion that Goniopora may benefit from Iron/Manganese supplementation. My own anecdotal evidence supports this, as my specimen has an increasing number of tentacles which are substantially longer than they were initially, on indeed in most photos I have seen of the variety.
Goni's are one of those corals that either goes really good or really wrong! I kept one when i had softies before going to SPS my first attempt was failure but I also didnt have a fuge at the time my second attempt was awsome .. kept it going for 2+ years before I switched to SPS I didnt target feed but i broadcast fed using marine snow and marc wiess black powder had awsome coloration from this.. just my 2 cents
Good luck with your Goni they are really nice corals
