Sound like it might be diatom algae to me. Maybe post more info such as water parameters, how long you keep the lights on, how big is your clean up crew if you have any at all... maybe even post a pic if possible. HTH
To get rid of cyano you may want to try a few things from this list below:
- Start using RO/ water if you don't already
- Maintain water changes and increase the water change by a little bit
- Increase the amount of flow and make sure there aren't any dead spots in the sandbed
- Make sure you'r bulbs aren't gorwing the cyano. Old reef lights or cheap house lights can cause cayno
- Get a sandbed crew to mix up your sand and keep it clean