I've used ChemiClean for years and never had any problems with any of my fish or corals while in use. I believe this is either user error or something else is seriously wrong with your tank that you simply aren't aware of.
When it comes to livestock dying my first piece of advice is always to try doing a water change before anything else. It helps get your tank back to the initial balance that you had before things started going wrong.
If you have a lot of cyano, you need to figure out what is causing it. Feeding too often, not enough water changes, etc...the root of the problem is the solution to taking care of the issue.