In my experience in keeping saltwater tanks (over 20 years) I have formed a hypothesis. I'm not going to write a book this morning, so, we all know to limit excess nutrients and to have some sort of nutrient removal (regular water changes, aggressive skimming, or better, growing macro algae, also.) To make this short and sweet, my concern is detritus related. What I call the "vicious cycle", dead algae = detritus = more algae. What's important now that you have dead algae is detritus removal. Create lots of flow in your tank, step up your small water changes, syphon out all detritus you can get to. We all know that algae problems are directly related to poor maintenance. I know this because I am just a guilty as anyone else.