That's funny that you brought this up....because I've been picking up about 25gallons a week at...........I'M certain it's the same place you described and I have been noticing cyano on my sand too....

I bet this is the reason for the unwanted cyano popping up. I've been scratching my head about it for a few weeks now.

Thanks for posting.

Dang, I really need to get an RO unit already!