New sand or old Tony? You said you were rinsing it then stopped. My experience has been anytime that I have tried to add sand it has caused a small outbreak. Maybe the bacteria is colonizing that area? Don't know really. Kind of like a new restaurant is always busier than the old ones for a while.

I started getting some breakouts on my sand bed and what I have started to do again is stir and siphon the sand bed to help clean it while doing water changes. Seems to be keeping the cyano out breaks I was having down to a minimum. Only thing I would worry about is if you have a deeper sand bed in the display. I purposely kept my sand bed at 2" or less.