Hard to tell from photos but dinoscsn be a real pain. Low nitrates and phosphates will starve them out. Siphon out what you can with water changes also.
It is Dinos, don't do water changes as that will only make them worse. Siphon what you can through a filter sock. Keep on top of it everyday. That is how I beat them when I got them.
Its probably cyano. People typically confuse the 2. To get rid of it, reduce nutrient levels through various export methods. Don't reduce feeding if its at a level that keeps your inhabitants healthy.
No water changes. And dr tims refresh and waste away. The bacteria out competed the Dino. I added filter sock at the bottom of over flow and cleaned them every day. Took about 4 weeks. Water is still clean and perfect