I had this happen as well, could never figure out what exactly caused it, didn't kill any fish just a few corals. Best I can tell, it was the food I was feeding, I managed to beat them off eventually by cutting feeding way down, and only feeding right before lights out, then I actually increased the photoperiod on the DT. This was actually SM's suggestion, the theory being that it allow the corals to photosynthesize the nutrients out of the water. It seemed to work.

Scrubber during this time was growing very dark growth also, with a slimy dark brown dino type of coating, screen was 20x7 on a 120g tank with 4x 24W 2700K T5HO. Scrubber growth remained about the same after the dino outbreak was past.

It could have been overexposure on the scrubber also in my case though. I never made that connection until I started up my UAS test box, and I got a whole lot of dinos until the GHA started to really grow in, and then the dinos would kick in with too long of a photo period.

I would put 1/2 of the old lamps back in and see if that helps