I have had a 30 gal saltwater tank for a little over a year. I had a 70 gal but after losing too many expensive fish to weird happenings(psycho crabs, stressing out, pregnant crab polluting water

) we converted it to a freshwater tank. So anyways I only have hermit crabs and damsels in my 30 gal right now but I want to get a new fish tommorrow. I havent been able to get a "cool" fish for a long time because I had this mean but awesome calico crab (big guy) that would eat all the sand dwellers or anything that was slow. SO thats why I only have damsels. BUt he passed away

. It was sad because we had him a year. BUt now its been several weeks and the tank is ready for a new fish. Anyone have suggestions? I LOVE gobies, they are my favorite. But I need something small and semi aggressive that can go well with damsels.