If the rock is new it’s going to go through the ugly stages like all new tanks do. I’d try waiting it out for a month and see if it got better. If it doesn’t try removing that new section and cycling it in a another container.
Good point since i lost a big fish(power brown tang)before all these brown algae pop up. All events happened after added 5 more lbs rock from an online store (initial batch obtained from LFS gave no issues).