Just to let you know, I had problems with algae of different sorts until my tank was 9 months old, which was just a couple weeks ago. Then, BAM, like magic, no algae. (I had thought it was 7 months until I remembered it was set up 2 months before I joined this site. ) I think tanks cycle faster in regards to fish than they do in regards to plants/algae.
From what I've been learning, 1.4 WPG on a 90 gallon is at least the low end of medium light. A 4.3 WPG burst for 6 hrs may be too long. I'd cut the total photoperiod from 10 hrs to 8 hrs, and only run the burst for 4 hrs.
I've had this, any every other, kind of algae. SAE's and Black Mollies ate mine, and learning how to balance ferts and lights kept it from coming back. You can spot treat with excel, but that's only a quick fix and won't keep it from returning.
Anyone else got some info?