With the absence of a skimmer, there's a pretty good bet there's a good deal of dissolved organics in the tank water. High nitrates are likely fueling the growth of cyano even more.
I would suggest ditching the filter sock. With it trapping uneaten food for a week, that's likely contributing to the high dissolved organics and nitrates. With it gone, food that goes over the overflow will get recycled back to the tank and eaten - if not by the fish, by the clean-up crew. Your video also suggests very little in the way of coralline algae, which is not quite right for a tank that's going on 11 months, and leads me to think that the alkalinity and calcium haven't been consistently at >7 dKH and >380 ppm, respectively. I'd suggest consistently keeping the alk at 8 - 9 dKH and the calcium at 420 ppm or so, which will encourage coralline algae. To some extent, it will compete with the cyano for nutrients.
Finally, if you want the cyano gone, you can black the tank out for 3 days. That means actually masking off the glass with cardboard, and putting a temporary cover over the top. The cyano will be completely gone after 3 days when you take the cardboard off, but it may come back if the water still has high nutrient levels. However, it may help you get ahead of the curve on cleaning up detritus in the sandbed and rocks and getting the nitrates and dissolved organics down with water changes. The corals and fish will be fine with this, btw.
