SPS (small-polyp stony) corals — acropora, montipora, birdsnest — are the high-light, high-flow branching corals that demand pristine, rock-stable water; the advanced tier of the hobby.
They punish parameter swings harder than any other coral, so they belong in a mature tank with steady alkalinity, calcium and magnesium and low-but-not-zero nutrients. Acclimate every frag to strong light slowly to avoid bleaching.