imo please do yourself a favor and give that rock an acid bath. IT is loaded with phosphate right off the bat. Then dont use gulf rock to seed unless you can get a piece from someone else. Dont get it right off the boat. Ime that stuff is loaded with pest algaes and little in the way of beneficial critters. Ive never gotten a piece that didnt sprout at the least, halimeda and hair algae plus this was after a month in the tank with no signs of it all that time, then bamn, algae bloom. I will say, its coraline is the most beautiful though.
If I were you I would go to the store and find a barren looking piece at the bottom of the bin, scrubb it off then put it in a container of water with a strong light on it and see what comes out of it over a week or two. If nothing bad, then use it to seed.
Of course im paranoid beyond belief so take this for what it is. FYI, if you get live rock, period, you risk adding pests. Why not just use bacteria and the small amount of coraline on frag plugs for seeding?