dirty rock

I have been battling with this algae im not sure if its dinos or cyano or what but i have been doing weekly water changes but it just doesn’t seem to go away does anyone have any suggestions on what I could try? Even just identifying what it is so i can at least get an idea on what im dealing with

For those who don’t know, I recently got someone else’s established 20gal set up with two clowns and a blenny as a complete beginner. This forum has been a godsend and I appreciate you guys so much. Now for todays question: how do I clean these rocks? Will scrubbing with a toothbrush in clean...