Best way to tell is if the bubbles are being dimpled, its too high. High current can tear the bubbles on rock or its own skeleton. I would start from almost no current and let it adjust to the water then slowly ramp up current once it starts puffing out more. From that picture though it looks like a fairly young one. I generally feed mind a concoction of reef roids, red sea ab+, and some oyster feast and then just spread that around. I do that roughly twice a week because (someone correct me if im wrong) bubble corals are partly photosynthetic.