The great thing about acropora corals is that they do growo in different environments in different ways. In order to achieve your best colors, you should work the balance of your nutrient levels. It takes a balance of nutrient removal (silicates, phosphates, nitrates, plus others.....) and a great food source in order to keep the bright colors while not stripping the food source from the reef.
Keep in mind that with all corals, there is a unique symbiotic relationship between the algae (tissue) and the polyp. The algae creates its food source from photosynthesis in organelles called coralites. The waste alone does provide a food source for the polyp living inside the skeleton. However, this polyp can also grow significantly (Polyp Extension) by eating the zooplankton off of the water coloum. Adequate flow helps pass fresh zoaplankton to the acropora. This is why you always see great polyp extension at night.