That seems to be the common thread in what this is. Bacterial. But we don't carbon dose or run bio pellets. Closest thing is seachem mattrix which us rinsed every 3 months to remove detritus. I am going to get a larger return pump & see if increased circulation helps. Although I am reluctant to do this as I always have 0.00 nitrates so the flow through sump at moment is working really well to consume nutrients. Just really don't know what to do from here. It came back 2 days after the video ! Urghhh.