I would normaly agree.. until I had my experience with cyno. Sometimes it just does not work that way. I did everything one could possibly do other than buy a completely new system
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From what I was told and read is that sometimes cyon can become an "infection". It takes all it needs straight out of the air. Your water quality could be excellent and it would still flurish. I used a product called Chemi-Clean to kill my cyno and it is now gone as well I have no other algae problems, the tank is running beautifuly.
IMO: if all else fails, do what you have to do.
Chad