There are many strategies to control Dinophlagellates, but adding Chemi Clean is Not one of them. Chemi Clean is to control Cyanobacteria.
Actually, since Dinos and Cyano may look alike to many, you should start with proper diagnosis. Are you surre that you have Dinos, not Cyano?
Pictures of the tank under white light would be of some help, but microscopic diagnosis if available and feasible would be even better.
Controlling phosphates is always a good idea, but in your case they are not sky high and if so, you should lower phosphates gradually.
I presume "light Carbon" is an activated carbon? If so, by all means, run it.