I have this same dilemma, though I don't have grass yet. Have you heard of this species? Parablennius marmoreus? Called the Seaweed blenny. It's a local species, gets about 5 inches long, a little less. Eats vegetable matter. Requires a tank with high amounts of micro algae in the tank. Diet can be supplemented with Spirulina in dried and frozen form. Was looking up fish in my guide and found it. I wonder if John over at reef cleaners can dig this one up. It says it'll nip at stoney corals and clams, but I'm not keeping any of these. Don't know how far you intend to go with corals. I'm not going past softies. I know also Emerald crabs will eat this micro algae too, but I'm super concerned about adding an emerald crab with all the macro algae and seagrasses I'll be having. Either that or jawfish for sand sifting, but jawfish are predatory, the blenny is a vegetarian. What do you think? I'll post this over at Reef central too. Maybe we'll get some imput.
I like the shrooms too. They look great under the actinics. I think zoas will look stunnin as well, as will the Ricordea florida. It's taking shape, it's just an algae mess right now. And I do big water changes too, just not 90%, but I don't have seagrass yet.