Imo looks like bugs. something has to be picking at it. also keep an eye on the fish possibly? Friend of mine had an african cleaner wrasse (yellow tail species) and he was an sps muncher... every night he noticed a frag or colony getting disfigured or polyps looking "eaten" then that branch would die. stayed up one night to find the wrasse going to town picking at the sps at night... might be a stretch but more so saying look at night and see if anyones snacking invert/fish wise... otherwise I run my tank with sps as the dominant coral at 77-78 degrees, no higher. Maybe its the temp, doubt its the flow with that setup and everything else looks rather healthy and growing, but hopefully you find out whats going wrong and can fix it and salvage those corals before they finish themselves off!