I know how you feel...well kinda cause I only have a 37 gal
I had cyano
and diatoms all over my tank in the beginning and no matter how long I had the light off for, the cyano
would never go. Even off of the rocks. Syphoned and turning sand over didn't matter BUT my best friend the sleeper goby helped:] He made all the orange sand disappear with his sifting and picked at the rocks when he was done so if your tank is safe enough, try a goby.