I would focus on your nutrient export and then try another round of chemiclean or similar products. How are you exporting nutrients today? Is your skimmer working and big enough for your bioload? Are you using GFO/carbon or carbon dosing? This will be your long term fix. The chemiclean should buy you some time.
You need to be VERY careful with chemiclean and following the dosing/instructions exactly or you can crash your tank with oxygen depletion or other nasty side effects. I've been able to remove 99% of big cyano blooms doing this.