Time and consistency.
Algae is there in some form with every tank -don't sweat it.
I too lost my first piece of red dragon and have no idea why. now it grows like a weed in the exact same tank! In my experience, a truly settled tank is the key to success with SPS. Established LR, a refugium that is as large as possible, and stability in husbandry are the keys to success; not high-priced hardware.
Don't give up! In a few months hit me up and i will give you some more red dragon to grow out