I'd bump your SG to 1.025-1.026,lower salinities can be stressful to reef inverts/corals.Most of all though,increase your flow.you need to be at 750gph(25x) inside the tank with multiple water outputs(at least 4 IMO).My guess is your filter(Cascade1200) is causing this water quality problem.I didn't see any mention of a skimmer either