I would not use Chemiclean.. Most chemicals only put you on a Cycle of Dependency.
Cyano can be handled effectively with proper filtration, Water changes, Increased flow and Changing out Micron filter pad or socks daily.
Since you have it so bad
1. Prep for a large water change
2. Install 50 micron filter socks or as dense as you have.
3. Using a Hose and a Bucket Vacuum as much of it as you can off the rocks and sand bed.
4. Using either a power head in your hand or a turkey baster ( power head is best what i use ) Blow the rocks clean.
5. Do your water change before it settles again..
6.Increase flow aiming the power heads at rock work and sand bed as much as you can without a sand storm.
7. Change out the Filter media as needed to collect the debri from water Column..
8 Do this every few days until its gone.
GET A Good steady maintenance routine that keeps it gone and stick with it.. It will help other things as well not just the Cyano..
Good Luck