Whats wrong with my efflo ??

[Stones]

As dreef already mentioned, check to see what your Mg levels are at as STN from the tips down is often associated with a Mg shortage.

Running only a 2 bulb T5 fixture is likely also not enough light for your aquarium. To sucessfully maintain SPS under T5's, most people typically run either 6, 8 or 12 bulb fixtures. Personally, I feel that a 6 bulb fixture would be a little on the weak side to keep SPS happy and healthy.

Also, I'm pretty sure that you've misidentified your Acropora. An A. efflorescens is one of the few plating species of Acropora and typically looks like this:


They are an extremely sensitive and tempermental species of acropora that often take years to color up and can sit for prolonged periods of time without growing or changing color. They brown out from changes in nutrient levels, changes in light or rapid changes in alkalinty very easily as well.