Blackout works great on the cyano in my salt tank. I don't know about the entire substrate ecosystem in most planted but I also got a TON of snails to stir up the sand might work for you BUT.. I doubt you want a million snails on the glass lol!
Oh yeah another thing is cyano almost always has bubbles under a green, blue, or red film
Iv never seen freshwater cyano before though.. Best of luck!! I would be so angry haha like I am with my bba problem >.<