Hey Kyman,
I had a cyano problem, that once cleared itself up and turned into a diatom problem. It covered my sand and rock.
I basically just upped my water changes to weekly. I have a 29g, and I changed 5g per week, I added a skimmer and some phosban media in a media bag into my sump.
It took a few weeks, but the problem subsided on its own. It's a natural part of a new tank cycle. Albeit, now my diatoms have turned into hair algae! Haha!
During all that time, I just made sure to keep my filter pads and any filter floss clean as well as continuously rinse off any debris that gathered on my media bags.