I have to side against the chemical treatment as well, we were frustrated with the cyano in our 55g, so we used Chemi-Clean, did it work, yes (wiped out 99% of the stuff overnight), did it do other harm.... we believe so. There have been a few good write ups about it around here somewhere. Basically the chemical approach, is to dose your tank with an antibotic, namely Eurethramyacin (sp?) aka Emyacin, IMO it has to kill the good bacteria with the bad. Followed by a 50% water change I think after 24 hours.

No thanks....never again, I'd rather suck cyano through a straw before going that route again... patience and persistance... it's a battle that can be won.