coral problems

for some reason I can't seem to keep corals.....I have tried 3 of them so far, and they all keep dying. I have done everything correctly as far as I know of.....is there any secret? I dose with Iron, Calcium, Iodine, and Coral-Accel. the tank is at 78 degrees, and my bulbs (2 10K & 2 Atenics) are only about 2 months old....I have no idea what there is to do. everything else is doing great.
 
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